Picked up this sign at Columbus and was wondering if anyone had seen one like it before?



It's marked "IR 56" at the bottom and is the same size as many other Mobil shield pump plates - 12.5" x 12.5"



It's shown here beside a Mobilgas PPP, with two smaller truck cab-top signs above. Someone suggested it might be a truck door sign, which makes some sense to me. The only truck door signs I've seen are shown below.....if this is one, then I'd expect a right-facing mate to be out there somewhere.



I got it from a well known collector who found two of them 15+ years ago. I'd appreciate hearing from anyone who has this sign or knows how it might have been used.

Richard