WDIV is an easy guess. D for Detroit and IV for roman numeral 4 [[channel 4).

Amazon Echo [[Alexa) has a problem recognizing WWJ. It plays some other radio station instead. You have to tell it to "play WWJ News Radio." I'm just guessing the three-letter call letters confuses it.

Plus what ndavies said about C, K & W. I didn't know about the kilowatt and watt significance. Makes sense though.