GARGOYLE Mobileoil Sign

This is a sign that Gary found when digging a hole in our back yard, was buried down about three inches covered with soil and weeds. We are wondering the approximate date or age of it. We are also looking for the value. We have lived in this house since 2003, it was built in 1942. The sign had to have been there a long time, but as you can see it did not rust very much at all. The orginal owners of our house built it and worked on semi trucks, farmed, and logged trees.
If you can estimate the age, please contact us.