In the US, radio and tv stations use K or W and amateur radio operators do as well.
If I recall, K was the west coast and W was the east coast.
That's why you'll see WNBC in New York and KNBC in California.
In the Dallas/Fort Worth area in Texas, we have WFAA (a TV station), WRR, WBAP (radio stations) and all the rest that I can recall are K. I guess since we're in sort of the middle we have them both. (Though far more K)
The W stations are typically older ones here.