Hi Ram,
I have also seen this on ebay recently. In general, Mobil used the open a before 1946 on signs. That is also when they started with the 12x12 inch shields. Before that, the gas pump signs were not shield shaped, but the small rectangular or the keyhole type (Mobilgas ask for Mobiloil). The only Shields I have seen that were dated before -46 were the large ones hanging on, or standing on a pole (5X5 feet or so)and a 12X12 inche shield with the Pegasus facing right (it was said to be one of four known). Another thing is that the text under Mobilgas normally is red (diesel, special, Marine, Gasoline...)
This sign is a bit odd as it has both the open a and black aircraft text, but it looks "old" in the picture. Sorry I cant give you any more details. Anyone else that can spread som light on this?
regards,
Claes