In style, almost looks older than WWI, but that is probably quite improbable. If CBG didn't know right off...........................Must be super rare!
I asked someone over at http://www.allexperts.com and this is the response I got about your pin.
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The Quartermaster's Corp used a similar motif but it was an Eagle atop a wheel, and the wheel is crossed by a key and sword.
My best guess is it is the emblem worn by a motorcycle dispatch rider. Some 20,000 motorcycles were used by the US Army in WWI. There were motor cycle units assigned to various services, the Quartermaster Corp, the Signal Corp, and even some Machine gun bearing motor cycle units.
You might contact the US Army Historical division and see if they can tell exactly what unit might have used this device.
I contacted Scott at Bay State Militaria and below is his opinion. Hope it gives someone a lead. Good luck!
Hi Tim,
I think it is a type of insignia for a driver for the American Red Cross or other volunteer organization made up of Americans. I have seen other similar items, so I think these may have been sold commercially in France during the War.