Hello Bob, Welcome to the forums!
While I can't personally help you with the Pauls Valley call sign, you might check out the link I've provided to the Morse Telegraph Club. Possibly someone there could answer your query.
I became involved with a similar project here in my adopted hometown of La Plata, MD. I discovered that the call sign was "PA". The local Charles County Amateur Radio Club meets monthly in the La Plata Train Station Museum. As recompense for utilizing the station as the meeting room, one of the members put together a Morse sounder. However, he felt that the simple "PA" was just too short so the sounder spells out "La Plata" for the entertainment of visitors. However "Pauls Valley" would most likely be too long to spell out in Morse Code.
Here's a link to a long dormant thread in the "Railroad Radio and Communications" forum regarding the use of American (Or "Railroad") Morse Code:
http://www.railroad.net/forums/viewtopi ... =43&t=4317
Art Audley, AA3RT
Moderator: Railroad Radio & Communications, Railroads in Books, Magazines, Music, TV and other Media, General Discussion: Fallen Trolley & Interurban Lines, General Discussion: Shortline, Industrial & Military Railroads,