What is this US Army Pin/Device/Insignia?

I was visiting my parents last week, and in the process of filling in blanks on the family tree, my father brought out his father’s service records from WWII. Grandpa served honorably but unremarkably, so there’s not a lot there. Among the paper records was a leather packet with Grandpa’s medals and ribbons, and there’s one I can’t identify.

Here’s a photo of the thing I can’t identify. It appears to be a lapel insignia of some kind.

If it helps, Grandpa was a driver/mechanic and also a theater projectionist. At least part of his service was with S.C.U. 1913 - Medical Division at Camp White, Oregon. His discharge papers show his MOS as “Projectionist 137.” The section for “Decorations and Citations” lists:
[li]Good Conduct Medal[/li][li]American Theatre Service Medal[/li][li]Victory Medal WWII[/li][/ul]
It clearly isn’t any of these. His discharge was in Feb. 1946 for “Convenience of Government RR 1-1 Demobilization AR 615-365 15 DEC 44”

Anyone know what this is?

Transportation Corps.

Transportation Corps insignia:


Thanks everyone! I assumed it was something like that, but didn’t have any idea how to find it on the web.

Specifically, it’s for an Enlisted member of the Transportation Corps. The brass circle backing the corps insignia indicates Enlisted.