I have a Mobilgas Shield sign from a station, but it is not a familiar design to me. I have not been able to locate it in any publications, and was hoping for a little assistance.

It is a large double sided porcelain sign with both the Pegasus horse, and the text Mobilgas. Also, it has a white star with a blue circle surrounding it toward the bottom center of the sign. The only dates I can find are at the bottom of the sign and read R33.(I believe that there is a letter before the R, but most of it is missing, it may be "N".

Any ideas when this sign was used and ideas on value? I can email photos if you need them. Thank you.