Found in an unpaved parking area of an old football field that hasn't been used in several years. Both sides are the same if flipped over vertically, in the photo it's flipped horizonally. It's a little larger than a quarter, chrome plate over brass and the grooves appear to be identical on both sides. Maybe some kind of key?
[attachment 81354 whatzit2.jpg]
[attachment 81354 whatzit2.jpg]