May I ask you where you found it? If it was in an area used by US troop during the WWII time frame, that might help narrow the possibilities. My first thoughts were the AG (Adjutant General) Corps or maybe an aide-de-camp button.
It was found on an old farm with mostly pre 1900 coins etc. There was an Australia shoulder badge near it so it may have been brought back from ww1 as a souvenir perhaps. When the ground dries out I'm planning to head back out to the site and go over it again.