I found this pin today while coin shooting in a yard. I thought it might be Army Corps of Engineers but the brick building is different. I don't have a clue what it is for.
Looking at the back of it, it appears that it had a pin on the back, and looks like there was also more to it that had rusted off. I kind of like it, but I would say it is not a button . More of a broach? type of thing.