Hi Don,
I have not seen that sign before myself. The Mobilfuel Diesel globe of similar design dates from 1935-1962 according to the globe book. While I can spot 2 holes on either side, I could picture that piece as a curb sign due to the size, being double sided, and the obvious shape. The material also makes sense IMO, as there were far less stations selling diesel fuel, so making them in tin was a lot less expensive than having porcelain signs made. I have never seen one in any period photos. I can't really see it being a reproduction item personally, but maybe someone else has some more information or has seen one.
Darin