Callsigns in North America are frequently still used by North American broadcast stations in addition to amateur radio and other international radio stations that continue to identify by callsigns around the world. Each country has a different set of patterns for its own callsigns.
Many countries have specific conventions for classifying call signs by transmitter characteristics and location. The call sign format for radio and television call signs follows a number of conventions. All call signs begin with a "prefix" assigned by the International Telecommunications Union. For example, the United States has been assigned the following prefixes: AAA–ALZ, K, N, W. For a complete list, see international callsign allocations.
Pertaining to their status as former or current colonies, all of the British West Indies islands shared the VS, ZB–ZJ, ZN–ZO, and ZQ prefixes. The current, largely post-independence, allocation list is as follows:
Cuba uses the prefixes CL–CM, CO, and T4, with district numbers from 0 to 9 to amateur operations.
The Dominican Republic uses the prefixes HI–HJ.
All of the French possessions share the prefix F. Further divisions that are used by amateur stations are:
Haiti has been assigned HH and 4V.
The island nation of Trinidad and Tobago use the 9Y–9Z prefixes.
Canadian broadcast stations are assigned a three-, four-, or five-letter base call sign (not including the –FM or –TV suffix) beginning with CB, CF, CH, CI, CJ, CK, VA–VG, VO, VX, or VY. The CB series calls are assigned to Chile by the ITU, but Canada makes de facto use of this series anyway for stations belonging to, but not exclusively broadcasting programs from, the Canadian Broadcasting Corporation. Several other prefixes, including CG, CY, CZ and the XJ to XO range, are available, but are not currently in broadcast use. Conventional radio and television stations almost exclusively use C call signs; with a few exceptions noted below, the V codes are restricted to specialized uses such as amateur radio.
Special broadcast undertakings such as Internet radio, cable FM, carrier current or closed circuit stations may sometimes be known by unofficial call signs such as "CSCR". These are not governed by the Canadian media regulation system, and may at times reflect call signs that would not be permissible on a conventional broadcast platform.
Four-letter call signs are the norm. Three-letter call signs are only permitted to CBC Radio stations or to commercial stations which already had a three-letter call sign before the current rules were adopted, and five-letter call signs exclusively identify CBC transmitters (which may be either rebroadcasters or SRC O&Os outside of Quebec.)
Stations of the Canadian Broadcasting Corporation or Société Radio-Canada tend to identify themselves as "CBC Radio One"/"CBC Radio Two" (English-language) or "La Première Chaîne"/"Espace Musique" (French-language) of a city, although they do have official three- and four- letter call signs. These generally (but not always) begin with CB.
Callsigns with four digits preceded by VF (for radio) or CH (for television) are only assigned to very-low-power local rebroadcasters; VO callsigns may only be used commercially by stations in Newfoundland and Labrador which were licensed before that province joined Canadian Confederation in 1949 (VOCM, VOAR and VOWR broadcast from St. John's long before Confederation). Only one station, VOCM-FM, has been allowed to adopt a VO callsign after 1949; it was granted the VOCM calls because of its corporate association with the AM station.
All Canadian FM stations have an –FM suffix, except for low-power rebroadcasters which have seminumeric VF callsigns. Higher-power rebroadcasters are generally licensed under the callsign of the originating station, followed by a numeric suffix and, for FM rebroadcasters of an AM station, a –FM suffix; for example, CJBC-1-FM rebroadcasts CJBC (860 Toronto), whereas CJBC-FM-1 rebroadcasts CJBC-FM (90.3 Toronto). Some rebroadcasters, however, may have their own distinct callsigns. Canadian TV stations always have the -TV suffix, with the exception of those CBC-owned stations which have a call sign in the CB-(-)T format. Canadian digital transitional television undertakings have -DT suffixes, even where the base callsign is a CBC/Radio-Canada O&O in pattern CB...T, CB...ET or CB...FT (for television, English language television or French language television, respectively). For instance, SRC's O&O CBOFT-DT would represent "CBC Ottawa Français Télévision - Digital Television". Canada does not use the -LP or -CA suffixes that are in use in the United States but makes limited use of -SW for privately-owned shortwave radio stations.
For rebroadcasters which use a numeric suffix, the suffixes usually follow a 1–2–3 numeric sequence which indicates the chronological order in which rebroadcast transmitters were added. There are some cases where television rebroadcasters are suffixed with the channel number on which the transmitter broadcasts (for instance, CIII-TV's rebroadcasters are numbered with their channel assignment rather than sequentially), but this is not generally the norm.
Experimental television stations in Canada have callsigns beginning with VX9.
The CG prefix is used by Canadian coast guard stations and ship-to-shore radio on federally-owned ships; Coast Guard Radio stations have also used VA through VF. Individual ships will use callsigns with a Canadian two-letter prefix (such as CF, CY, CZ, VB, VC or VY) followed by a four-digit number. The CY prefix is used by Canadian airports, while individual aircraft are identified with a prefix such as CF or CG followed by a five-digit number. Military radio fixed stations also bear callsigns in the CF-CK, CY-CZ, VE and VX-VY series. Environment Canada weather stations have calls of three letters and three numbers, issued from various C, V or X Canadian prefix series.
Canadian amateur radio stations generally begin with VE, some also use VA. The number following these letters indicates the province, going from VA1/VE1 for Nova Scotia, VA2/VE2 (Québec), VE3/VA3 (Ontario) through VA7/VE7 for British Columbia and VE8 for the Northwest Territories, with latecomer VE9 for New Brunswick. (VE1 used to be for all three Maritime Provinces.) VE0 is for maritime mobile amateur transmissions. VY1 is used for the Yukon Territory, VY2 for Prince Edward Island, and VY0 for Nunavut. CY0 and CY9 are Sable Island and St. Paul Island; with little or local population, reception of these distant points is rare, although amateur radio stations do temporarily operate from these islands during shortwave radio contests. Special prefixes are often issued for stations operating at significant events.
The Dominion of Newfoundland prefix VO remains in active use by amateurs in the province of Newfoundland and Labrador, VO1AA atop Signal Hill in St. Johns being the most famous amateur station. Radio amateurs on the Island of Newfoundland use calls beginning with VO1, while Labrador amateurs use VO2. A popular backronym for VO stations is "Voice of...", although prefixes do not have any official meaning.
Mexican broadcast stations are assigned a three-, four-, five-, or six-letter callsign beginning with XE (mediumwave and shortwave) or XH (FM and TV). Some FM and TV stations (like XETV) are grandfathered with XE callsigns and a –FM or –TV suffix. Mexican stations are required to identify twice an hour, at both the top and the bottom. Mexican stations broadcasting English-language programming are in addition required to play the Mexican national anthem every day at midnight local time. As in Canada, stations that rebroadcast other stations may have the same callsign, but with a different number at the end (such as XEMN and XEMN-1). More commonly, television rebroadcasters are assigned XH calls in the same manner as any other Mexican television station.
Amateur radio stations in Mexico use XE1 for the central region, XE2 for the northern region, and XE3 for the southern region. XF prefixes indicate islands. XF4 is usually used for the Revillagigedo Islands and nearby islets. Special callsigns for contests or celebrations are occasionally issued, often in the 4A and 6D series, although these will follow the usual district numbering system (4A3 for the south, etc.).
In the United States, broadcast stations have call signs between three and six characters in length, though the minimum length for new stations is four letters. An additional suffix may also be added, indicating a specific broadcast service type. Full-power stations receive four-letter call signs, while broadcast translator stations usually receive call signs with five or six characters, including two or three numbers. Generally, call signs begin with K west of the Mississippi River, and W to the east.
New full-power stations were formerly assigned sequential call signs if the permittee does not choose one of their own; these were always four letters, of which the third was the least-significant digit and the second was the most-significant digit of the sequence number. (Callsigns which were already assigned are skipped in the sequence.) Hence, many very early stations, like WMAQ Chicago (now WSCR) and WMAF Round Hill, South Dartmouth, Massachusetts (now defunct) were assigned W-A- or K-A- call signs. The current FCC rules require a permittee to explicitly select a callsign before putting a station on the air for the first time. Prior to that time, permits for new stations are either listed simply as NEW, or referenced by the file number of the original application, in the FCC's public records.
Deleted stations are listed in the FCC database with a D prefix for a while (such as DKXXX for the former KXXX), and are eventually removed from the database. D is not a prefix letter allocated to the United States.
Stations may change their callsigns whenever they like, and often do so in connection with a change of radio format. Callsigns become available again after 30 days of non-use, although stations (frequently under common ownership) can swap callsigns at the same time.
In the 1920s, many stations were assigned three-letter call signs; these have been grandfathered under the current system, even though many such stations have changed owners. Such stations include KOA in Denver, Colorado, WGN in Chicago, Illinois, and WRR in Dallas, Texas. (WRR is an unusual case in that the call sign was moved from the original AM station to a commonly owned FM station, formerly WRR-FM, before the AM was sold.) The Federal Communications Commission for many years maintained a policy of "drop it and lose it forever" with respect to three-letter call signs, but recently allowed KKHJ (930 Los Angeles) to reclaim its historic three-letter call, KHJ.
The FCC allows FM and TV stations under common ownership with a three-letter AM or FM in the same market to use five-letter (three plus –FM or –TV suffix) call signs; for example, KGO-TV in San Francisco or WMC-FM in Memphis. In some cases, such as WIL-FM in St. Louis, the five-letter callsign may outlive the three-letter call sign on which it is based. There was also the unusual case of Baltimore's WJZ-TV, which was allowed to adopt the call sign despite the fact that there was no WJZ radio; when there was, it wasn't in Baltimore; and it hadn't been owned by the same company since the 1920s. The callsigns WJZ and WJZ-FM were assigned much later (to commonly-owned stations in Baltimore). Stations which have been "conformed" in this manner may keep the five-letter call sign even after they are no longer co-owned with the "parent" station (although this was not the case prior to the mid-1980s). WWL (AM) and WWL-TV in New Orleans would be an example of eponymous stations no longer under common ownership.
Extremely early call signs used in the 1910s and into the early 1920s were arbitrary. The U.S. government began requiring stations to use three-letter call signs around 1912, but they could be chosen at random. KDKA initially broadcast as 8XK before gaining its well-known letters in 1920. The Rosicrucian Order, AMORC of San Jose, California used the call sign 6KZ.
New broadcasting stations are assigned call signs beginning with K, if they are west of the Mississippi River, and beginning with W if they are east of the river. No broadcast stations are assigned call signs beginning with N or AA–AL. Again, some early stations have been grandfathered, so there are four broadcasters with a K prefix east of the Mississippi, and a few dozen with a W on the west side. (There are more grandfathered W stations because the dividing line used to be two states farther west.) Some examples are KDKA in Pittsburgh, Pennsylvania, KYW in Philadelphia, and WACO-FM in Waco, Texas, which also has the distinction of being one of only three radio stations whose call sign is the same as its community of license. Stations located near the Mississippi River may have either letter, depending on the precise location of their community of license and on historical contingencies. Minnesota and Louisiana are allowed to use both call letter prefixes since the Mississippi river flows through both states in addition to forming parts of their borders. Metro areas that straddle different states on both sides of the river, such as St. Louis, Memphis, and Quad Cities area of Iowa/Illinois, have stations with both call letter prefixes, due to the stations' communities of license being placed on either side of the river. 
The FCC allows derived call signs in the same market as a commonly-owned AM or FM without respect of the boundary, so stations may establish common branding across bands and services. One famous example was the case of the former KWK in St. Louis, which after several petitions was permitted to change the call sign of its sister FM station in Granite City, Illinois, then WWWK (FM), to KWK-FM. Later, the AM would change its call sign and the FM became KWK (FM), thereby becoming an exemplar of both categories of grandfathered stations.
The assignment of K and W prefixes applies only to stations in the broadcast radio and television services; it does not apply to weather radio, highway advisory radio, or time signal stations, even though these are all broadcasts in the usual sense of the word, nor does it apply to auxiliary licenses held by broadcast stations, such as studio-transmitter links and inter-city relay stations.
For example, the time signal stations WWV and WWVH are located in Colorado and Hawaii, respectively. (WWV originally began in Maryland and was later moved west. However, even ignoring that fact, U.S. government-owned stations are overseen by the NTIA and not the FCC, and are thus not subject to the FCC's rules on call signs; most do not have call signs at all.)
NOAA Weather Radio stations clustered between 162.4 and 162.55 MHz have call signs consisting of a K or W followed by letters, and two digits. The K and W prefixes are both used interchangeably on both sides of the Mississippi River (e.g., KHB36 in Washington, D.C. and WXK25 in El Paso, Texas).
Highway advisory radio stations scattered throughout the AM band use call signs consisting of K and W followed by two or three letters and three digits. As with weather radio, K and W calls are both used on both sides of the Mississippi River.
Call signs in the western United States are often confused with International Civil Aviation Organization (ICAO) airport codes because both make use of four-character codes that begin with the letter K. Examples include KSFO (which simultaneously refers to San Francisco International Airport and KSFO (AM) radio), KLAX (which simultaneously refers to Los Angeles International Airport and KLAX-FM), and KDFW (which simultaneously refers to Dallas-Fort Worth International Airport and KDFW-TV). On a related note, an interesting case is in Columbus, Ohio, where the ICAO identifier KCMH (Port Columbus International Airport) shares all but its prefix with local TV station WCMH's call sign.
FM radio and television call signs may be followed by a dash and the two-letter class of station: –FM, –LP, –TV, or –CA. For digital television, the early –HD and later –DT suffixes are usually not used (one exception being KKYK-DT), as the digital channel is not usually licensed separately from the analog. (Beginning in June 2009, stations may choose -TV or -DT.) Some station owners using the iBiquity HD Radio IBOC system have expressed a desire for –HD call signs, but this is unlikely to happen because HD Radio is a sideband service on the same center frequency. Occasionally, an FM or TV station may have one or more boosters, which retransmit the main station's signal to overcome terrain obstacles. In this case, the main portion of the call sign remains the same (unlike translators), and the boosters are given sequential numeric suffixes like –FM1, –TV2, –3, and so forth.
It should be noted that the -FM or -TV suffix is not required to be assigned to TV or FM stations, except where there is another station that shares the same 3- or 4-letter base call sign with no suffix. AM radio stations never have an -AM suffix. Where a station has no suffix, the FCC uses parentheses to identify the station unambiguously in documentation (i.e. rulemaking proceedings), the same way Wikipedia handles disambiguation of article names (except that there is no space between the two). This ensures that [for example] WIKI (AM) is not mistaken for WIKI-FM and WIKI-TV just because it was identified as only WIKI. This occurs regardless of whether there is actually another station using the callsign.
Low-power TV and FM stations share the –LP suffix. Class A television stations, which are LPTV stations that receive protection from interference by primary stations, use the –CA suffix. When low-power and class-A TV stations operate in ATSC digital TV, they instead receive the suffix –LD. Although –CD was expected to be used for digital class A, stations do not appear this way in the FCC database.
FM and TV broadcast translator stations are assigned sequential call signs. They use an appropriate initial letter followed by a two- or three-digit channel number, and then a two-letter sequential suffix. For example, a translator on TV channel 4 might have the call sign K04AX (though it is much less common for TV translator channels to be between 2 and 13). Digital translator stations are assigned call signs in the same manner, except that the letter -D may be appended (e.g., K04AX or K04AX-D). The FM band also has channel numbers starting at the number 200 (or 201 for practical purposes), although they are almost unknown to regular listeners who usually tune in to a station based on its frequency. W201AA was the first FM translator at 88.1 MHz in the east, for example. Such call signs are never reused by another station, though it is unclear if this could occur in the future due to exhaustion of the 676 (26²) two-letter combinations. As of 2009. channel 13 in the west (where the Rocky Mountains make translators a necessity) is up to K13Zx. In this limited case, the X does not indicate an experimental station.
The FCC makes no differentiation between translating and originating LPTV stations, thus either type of station may have an alphanumeric or a regular -LP or -LD callsign.
Beginning in 2009, the FCC allows digital TV stations to apply for translator stations that are not given a separate callsign, instead taking that of the primary station. This is only in the case of areas that will lose coverage due to the digital television transition in the United States.
Many stations prefer not to use call signs at all, since a moniker or slogan is more easily remembered by listeners (and those filling in diaries for the Arbitron radio ratings). However, in the U.S., the Federal Communications Commission does require periodic station identification using the formal callsign, as close to the top of each hour as possible, at a "natural break in programming"; this rule is now rarely enforced. Stations are also required to identify their community of license. Only the frequency, name of the licensee, channel number, and/or network affiliation may come between the two.
HD Radio stations must identify "HD1" for their analog-simulcast channel, and "HD2" or "HD3" for other channels, however this is not part of the callsign. Translator stations only need to have their callsigns announced three times a day (at particular times) through the main station, or though some broadcast automation means (voice or Morse code) hourly by the translator.
There are some unusual cases, such as the low-frequency WWVB time station. Because of the station's narrow signal, that station only broadcasts a one bit per second signal that cannot usually be understood by humans, so the station is identified by shifting the broadcast carrier wave's phase by 45° twice an hour (see Phase-shift keying).
It is fairly common for stations to choose a call sign that can be transformed into a name, such as Boston's WXKS-FM (107.9 Medford), one of many Clear Channel Communications-owned stations that call themselves "KISS." In other instances, the letters may be an initialism for a name or slogan. Some of the most famous of these include WGN (WGN and WGN-TV), owned by the Chicago Tribune, which stands for "World's Greatest Newspaper", WIS in South Carolina, which stands for "Wonderful Iodine State," and WISN, which dually stands for the station's original owner, the Wisconsin News, and the station's location in Wisconsin. In Winston-Salem, North Carolina, the call sign WXII was chosen to represent the Roman Numeral 12 which is the channel on which the station broadcasts. Affiliates of the Big Three television networks (ABC, CBS and NBC) in New York City and California get their call signal from their network, with New York stations adding the "W" and Los Angeles or San Francisco stations adding the "K". Stations operated by schools and universities may adopt their school's "initials" into the call sign, such as WWVU in Morgantown, WV, the university-owned radio station of West Virginia University.
United States amateur radio call signs are issued with one or two letters, followed by a single digit, and then one to three more letters. Generally the shorter the call (up to a 1x2 or 2x1 format) the higher the grade of license, but an amateur who upgrades is not required to change his or her callsign. In any case some of the available blocks have been used up. The 1x1 callsigns, such as K6O, are for short-term special event stations. Outlying areas have special calls. For example, those issued in Hawaii can (like other U.S. callsigns) start with A, K, N, or W, but then will have H6 or H7 before the 1–3 additional letters. Other Pacific possessions use other H numbers; a Guam station could be KH0–. Alaska has L as the second prefix letter, and Caribbean stations use P.
The number in the call refers to one of the 10 radio districts into which the U.S. is divided, but that only indicates where the license was issued. It is no longer necessary for a U.S. ham to change callsigns when moving to a new district. Most amateurs going to an exotic location will sign/(prefix) to show their location. Thus a station visiting American Samoa could be (regular call)/KH8. American amateurs are also permitted to operate in Canada under their own call signs with a location indicator.
Amateur stations are required to identify themselves by their call sign once every ten minutes during a transmission or series of transmissions and at the end of the transmission.
Experimental stations use call signs out of the amateur radio sequence, with the letter following the region digit required to be an X. (All VHF TV stations before World War II were licensed as experimental stations.) Notable experimental stations included Major Armstrong's FM station W2XMN in Alpine, New Jersey; Powell Crosley's 500-kW superpower AM W8XO, operating nights only with WLW's programming and frequency from Mason, Ohio; and Don Lee's pioneering television station, W6XAO in Los Angeles. (Synchronous "booster" transmitters for AM stations are still considered experimental in the U.S., despite fifty years of experience in Europe, and new experimental call signs are being assigned for new licenses even now, by inserting a region digit and the letter X into the parent station's call sign.)
Puerto Rico, Navassa Island, and the US Virgin Islands all use the American standard call signs of W (being east of the Mississippi River). Guam and the Northern Mariana Islands use K. American Samoa uses K as well, but WVUV was grandfathered in, and remains as an AM radio station; the low-power TV station that was WVUV-LP changed its callsign to KKHJ-LP in 2008. All of these areas are under the jurisdiction of the U.S. FCC.
Callsigns are also used in other parts of the world, particularly those which have had significant U.S. influence at some point. This includes the Philippines, Japan, and formerly Australia. Another well-known callsign outside of the region is HCJB in Ecuador, and several time stations used to set radio clocks or for audible listening.
The rules governing call signs for stations in the United States are set out in the FCC rules, 47 C.F.R. chapter I. Specific rules for each particular service are set out in the part of the rules dealing with that service. A general overview of call sign formats is found at 47 C.F.R. . Rules for broadcast callsign are principally defined in 47 C.F.R. .