It's time for some signage! I'm posting several Mid-Continent and D-X signs. If you've got any others, please feel free to post them or send them to me by email.
The sign that Norm (cmeon66) posted (Diamond Gasolines - Motor Oil) was one of the older-style (1925-33. You can see an example of it in the service station pic on Page 1.
This version was used from 1933-46.
In 1946, this sign came into use, replacing the name "Diamond" for service station identification.
Several variants of this sign existed. It was made in various sizes, with single and double-sided versions. The above sign shows an earlier font style, while this later example (below) shows a pudgier font. It is dated 1955.