From my many visits to the Grand Canyon State, Cowtown, AZ, popped into my mind first, so that's where I narrowed my search. Yes, Cowtown (or Cow Town) in general brings up some references to things in and around (and of) Fort Worth, but a lot of other stuff as well. I didn't plow too deep, but didn't come across any connections to BNSF or railroading. Is "Cow Town" used verbally by BNSF personnel over the radio in the Fort Worth area, or the Midwest, or where? I've never heard it used west of the Rockies, and I monitor quite a bit. A nickname for sure, but I question whether it qualifies as a railroad nickname (even if it dates back to cattle drive days, and livestock being loaded onto railcars), any more than Lilac City, Rose City, or San Berdoo.