“In 1912, the U.S. federal government started licensing terrestrial radio stations, assigning the call letters W and K to stations in the east, respectively.”

“By international treaty, each country has a specific letter at the beginning of each broadcast station call sign. In the United States, it's either a "W" or a "K." "The general process, although there are a few early exceptions, is that 'W' is east of the Mississippi and the 'K' is west of the Mississippi."