Pistol Pete

Pistol Pete mural
on Fifth Street between Grand and Garfield
Laramie, WY

Pistol Pete is one of the mascots for the University of Wyoming. Obviously, the UW on the chaps signifies University of Wyoming. The OSU could be Oklahoma State University, Ohio State University or Oregon State University. Possibly, one of those three is significant to the artist or the owner of the building. 

Update: Oklahoma State University are also Cowboys. This cowboy drawing is also associated with their mascot. Thanks for the tip, Sara.