The pic almost looks like the lighting plays tricks on you. All I can provide is that it appears to have 'S.D' and '4'. The fact that the edges have a layer missing but it is still covered through the center of the item, it most likely isnt a button. As well, the fact there is much higher copper content in brass compared to the copper used in zinc pennies, and the size of it, I am sure it would be brass and ring up like a full copper penny.