Not sure of the origin of the KYW call, but my recollection is that when
Westinghouse bought the station in Philly, they brought the KYW call sign
from some place in Ohio. Cleveland sticks in my mind but I wouldn't swear
to it.
It was over 40 years ago and my biggest concern was getting out of the
fourth grade.
Here is a link with some info on origins of some radio and TV station
calls.
http://www.oldradio.com/archives/nelson/origins.call-list.html
Steve KW3A