...oh, I think your value would be more than that - I saw a much later Mobilgas sign like this sell for over $1000, a couple of times...this one is a better size IMO...

...the marking is probably 'IR 33', for Ingram-Richardson, 1933...

Looking for better Gulf items: signs, globes, cans and paper - especially porcelain Gulf flanges, and Gulf A-38 & A-62 ad glass...