They were user for a short period - between 1941 to 1946, and only by the east coast parts of the company.
From 1946-1962, the porcelain shield signs were used by the different divisions.

The Mobilgas has a 1941 date and the special has a 1946 date and there is also a difference in appearance as the special Pegasus has a blue out line. This became also present at the Pegasus on the shields (except on the west coast shields).
As I understand they were - in parallell with the rectangular tin signs used by Wadhams - the first pump plates used by Mobil. Before this there had only been decals.. pls correct me if I am wrong.

Br
Claes