MudGuard,

Joe has it right (as usual), but let me add my two cents worth. The rest of the letters were often selected by the station (the same naming system is used for both TV and radio). So here in Baltimore, Maryland we have WBAL (radio and TV) where the BAL was chosen to represent BALtimore. A public radio station is WTMD. It broadcasted, originally from Towson, MD (where MD is the abbreviation for Maryland). Sometimes stations chose the letters to give it a certain "sound" or to spell a certain word. I think there is a West Coast Rock and Roll radio station that uses the letters KROC (for K Rock!).

Big RiB (in full helpful mode)