Light bronze / silver prop finish on this British made U.S. Air Service collar insignia.
Many times confused with French manufacture, the British made insignia for American Air Service is a great example showing a light bronze finish on the wings, and the prop left in the bright, most likely a silver wash over brass. Pin back with open catch. Whether or not it is original to the insignia, there is a coat of shellac covering overall; showing chipping on the back. I believe it is original by the wear.
44mm wing span.