Very common on trucks. Just about every truck my grandfather had from the 50's to the mid 80's had the dealer name stamped in the bumper. That was in Colorado. I remember seeing almost all the trucks around Houston with steel bumpers also had the dealer name stamped in them.
Heck, just saw a truck on Saturday (mid 60's) that had Austin, TX and the dealer name stamped in it.
I think it went out of style in the late 80's early 90's. My bet is they stopped shipping them from the factory without a rear bumper due to crash standards, thus they all had the same rear bumper.