What does the K and the W mean in front of radio stations?

Question

I realize that east of the Mississippi they use W and west its K, but why?

Answer 1

Intersting question..Never really thought about it.
It's probably just an FCC thing.

Found this:
http://ramblings.aaronballman.com/2006/04/Radio_station_naming_conventions.html

Answer 2

Radio stations starting with W are east of the Mississippi River, ones starting with K are west of the Mississippi.

Answer 3

There are a whole set of letters of the alphabet assigned for stations in various countries. Those happen to be the two letters that the US ended up with and assigned to radio stations in the east and west of the Mississippi.