American Television Station Call Letters
Call Signs or Call 'letters' have been assigned since 1927 by the FCC (Federal Communications Commission) initially to radio stations to identify them from all the different kinds of radio services over land, sea, air and space.
They serve three purposes, (1) identify the nationality of the station (2) the type of station (3) the individual station. Call signs, in effect, are like license plates of broadcasting.
Broadcast stations in the US are assigned call signs by the FCC beginning with K or W. Generally speaking, those beginning with K are assigned to stations West of the Mississippi River and in U.S. territories and possessions, while those beginning with W are assigned to broadcast stations East of the Mississippi River.
Since the beginning of radio broadcasting, stations have had the privilege of requesting specific call signs. In requesting their preferences for certain letters of the alphabet, broadcasters have presented combinations of names, places or slogans. For example, the letters NBC are used for stations owned by the National Broadcasting Company, CBS for those of the Columbia Broadcasting System, and ABC for the American Broadcasting Companies. Examples of individual station call letters are: WGN, Chicago ("World's Greatest Newspaper"), WNYC, New York (New York City municipal station); KAGH, Crossett, AK, ("Keep Arkansas Green Home"); WIOD, Miami ("Wonderful Isle of Dreams"); WLS, Chicago ("Worlds Largest Store"); WACO, (Waco Texas); WTOP, Washington, D.C. ("Top of the Dial"); KFDR, Grand Coulee, Washington, (Franklin D. Roosevelt); WCFL, Chicago ("Chicago Federation of Labor"); WMTC Vancleve, KY, ("Win Men to Christ"); WGCD, Chester, S.C. ("Wonderful Guernsey Center of Dixie"); Educational TV station WXXW, Chicago, uses the Roman numerals for its channel 20; and KABL, Oakland, CA, selected its letters to represent San Francisco's famous cable cars. If a new broadcast station makes no specific request, it is assigned a call sign by the FCC. Since 1946 the FCC has not guaranteed specific call signs to be granted prior to the grant of a construction permit or special temporary authority.
As broadcast stations began to increase in the early 1920's, the three letter call sign could no longer accommodate the growing number of stations, making it necessary to add a fourth letter.
With the advent of TV in 1941, new call signs for all such stations were not assigned. Rather, since many TV stations were operated by the same AM licensee at the same license area, the general practice was for the associated TV station to simply add "-TV", to the call sign of the co-owned AM station.
(Information from the FCC website - www.fcc.gov)