Was out this past Sunday with my dad, first time I've brought him with me. i currently use a whites coinmaster. I enjoy this machine. I'm a novice and I have found so much treasure! I can't imagine what I might be missing, and can still find once I upgrade.
It's a military button I know, past Civil War I think, and possibly from one of the World Wars. Don't quote me on any of this, as I'm still not anywhere near good with buttons, but someone else should chime in and tell you more closely what it is.
You could post to the "What Is It" forum for the quick answer, or search Google for historical military button websites.
There are a few of them that show buttons by mfg.
Ok, I did some research for you. It is made past 1941, so it would be WWII. The Same design was used since 1904, but the eagle faced to the right before 1941. Hope this helps!