Broadcast call signs
Broadcast call signs are call signs assigned as unique identifiers to radio stations and television stations. While broadcast radio stations will often brand themselves with plain-text names, identities such as "cool FM", "rock 105" or "the ABC network" are not globally unique. Another station in another city or country may (and often will) have a similar brand, and the name of a broadcast station for legal purposes is normally its internationally recognised ITU call sign. Some common conventions are followed around the world. North America. Broadcast stations in North America generally use callsigns in the international  series. United States. In the United States, the first letter generally is "K" for stations west of the Mississippi River (including Alaska, America Samoa, Guam, Hawaii, and Northern Mariana Islands) and "W" for those east of the Mississippi River (including Puerto Rico and the U.S. Virgin Islands). Except for those with their radio channel or physical TV channel number in them, all new callsigns have been four letters (plus any suffix like -FM or -TV) for some decades, though there are historical three-letter callsigns still in use today, such as KSL in Salt Lake City and WGN in Chicago . Co-owned stations were also allowed to adopt their original short AM callsign like WGN-TV and KSL-TV, even after new ones were prohibited. There are a number of exceptions to the east/west rule, such as KDKA in Pittsburgh and WFAA in Dallas-Fort Worth, but these are historical artifacts grandfathered from a rule change in the 1920s. Most of the exceptions are located in the media markets immediately adjacent to the river, in the state of Louisiana in the metropolitan areas of Baton Rouge and greater New Orleans, and markets north of the river's source such  as Fargo-Moorhead and Duluth-Superior. The westernmost station in the continental United States beginning with W is WOAI in San Antonio. WVUV-FM in Fagaitua, American Samoa, is the westernmost station with a W call sign. KYW in Philadelphia is currently the easternmost station with a K call sign. Another exception to this is that NIST time-broadcasting stations have a three- or four-letter callsign beginning with WWV. The three current government-operated time stations, WWV (and longwave sister station WWVB), and WWVH, are located in Fort Collins, Colorado and Kekaha, Hawaii, respectively, both of which would normally  use call signs beginning with "K". However, the rule dividing W and K only applies to stations governed by the Federal Communications Commission (FCC), whereas U.S. federal government stations are governed by the NTIA. This means that like NIST, the hundreds of NOAA Weather Radio stations across the country have a random mix of W and K callsigns, as do traveler information stations operated by the National Park Service. International shortwave. The US government-operated international broadcaster the Voice of America no longer uses callsigns assigned to it; however, Radio Canada International's transmitter in Sackville, New Brunswick was assigned  CKCX. Privately operated shortwave stations, like WWCR and CFRX, also have call signs. Canada. In Canada, the publicly owned Canadian Broadcasting Corporation uses "CB"; privately owned commercial broadcast stations use primarily "CF" and "CH" through "CK" prefixes. Four stations licensed to St. John's by the Dominion of Newfoundland government (VOWR, VOAR-FM, VOCM, and VOCM-FM) retain their original "VO" calls. The "CB" prefix used by CBC stations actually belongs to Chile rather than Canada, and is in use by the CBC through an international agreement. Low-power broadcast translator stations begin with "VF" for FM and "CH" for  TV, followed by four numerals assigned sequentially. Unlike the United States, all Digital TV stations use the "-DT" suffix instead of keeping the "-TV" suffix. Mexico. In Mexico, AM radio stations use "XE" call signs (such as XEW-AM), while the majority of FM radio and television stations use "XH". Broadcast callsigns are normally four or five letters in length, plus the "-FM" or "-TV" suffix where applicable, though several older stations have only three letters. The longest callsign is six letters, plus suffix: XHMORE-FM. All Mexican TV stations using Digital TV signals use the "-TDT" suffix. Central America . Costa Rica. Costa Rica uses "TI" call signs. Examples: El Salvador. El Salvador uses "YS", "YX" and "HU" call signs depending on geographical area. Examples: Guatemala. Guatemala uses "TG" call signs. Honduras. Honduras uses "HR" call signs. Examples: Nicaragua. Nicaragua uses "YN" call signs. Examples: South America. In South America call signs have been a traditional way of identifying radio and TV stations. Some stations still broadcast their call signs a few times a day, but this practice is becoming very rare. Argentinian broadcast call signs consist of two or three letters followed by multiple numbers, the second and third  letters indicating region. Brazil. In Brazil, radio and TV stations are identified by a ZY, a third letter and three numbers. "ZYA", "ZYB", "ZYR", and "ZYT" are allocated to television stations; "ZYI", "ZYJ", "ZYK" and "ZYL" designate AM stations; "ZYG" is used for shortwave stations; "ZYC", "ZYD", "ZYM" and "ZYU" are given to FM stations. Colombia. In Colombia, the radio stations or television channels are identified by HJ and/or HK with two additional letters. Examples: Venezuela. Venezuela uses "YV" call signs. Examples: Argentina. Argentina uses the letters “LS” followed by a two-digit number. Examples: Uruguay. Uruguay uses the word  CXB followed by a number as a callsign. Australia. In Australia, broadcast call signs are allocated by the Australian Communications and Media Authority and are unique for each broadcast station. The international VL prefix assigned to radio broadcasters has been skipped for many years, thus VL5UV would only identify as 5UV, and now simply Radio Adelaide. The digit often, but not always, indicates the state or territory, generally followed by two letters on AM and three on FM. Stations with call signs beginning in 2 are based in New South Wales or the ACT, 3 in Victoria, 4 in Queensland , 5 in South Australia, 6 in Western Australia, 7 in Tasmania, and 8 in the Northern Territory. Philippines. In the Philippines, stations may use callsigns in the following manner: callsigns beginning with DW and DZ represent all stations in Metro Manila and parts of Luzon. Calls beginning with DY represent all stations in Visayas, parts of Palawan and Masbate; and callsigns beginning with DX represents all stations in Mindanao. Originally from 1920 to 1940 callsigns beginning with KZ were assigned to all stations in the Philippines. Other regions. Most European and Asian countries do not use call signs to identify  broadcast stations, but Japan (JO), South Korea (HL), the Philippines (DW and DZ), and Taiwan (BE) do have call sign systems. Britain has no call signs in the American sense, but broadcast stations are allowed to choose their own trademark call sign up to six words in length. In Japan, Tokyo, Osaka, Nagoya and regions of Japan, television and radio stations as "JO__". Callbooks. A directory of radio station call signs is called a callbook. Callbooks were originally bound books that resembled a telephone directory and contains the name and addressees of licensed radio stations in a given jurisdiction (country ). Modern Electrics published the first callbook in the United States in 1909. Today, the primary purpose of a callbook is to allow amateur radio operators to send a confirmation post card, called a QSL card to an operator who they have communicated via radio. Callbooks have evolved to include on-line databases that are accessible via the Internet to instantly obtain the address of another amateur radio operator and their QSL Managers. The most well known and used on-line QSL databases include QRZ.COM, IK3QAR, HamCall, F6CYV, DXInfo, OZ7C and QSLInfo.