Looking for info on this old beauty

Can you dig it?! Out and about combing the local neighbor hood metal detecting & pops out this wonderful piece. Quarter sized brass with a screw on or pressed on back , button. On the front top is the beloved Eagle below it is a Shield with a Sword and a skeleton key. Not to shabby for the first hit today.. We're guessing it to be around civil war times... It was about 8" down reading as $.25 FYI only looking for some info we never part with the history we find.. Thank you very much, & love all the cool things I see posted!!