I'm not sure what pattern you are asking about. It looks like a flat button to me, with raised lettering around the back. If so, I think it is quite old, like 1700s. Late 1700s and later had indented lettering, as I recall. It looks like a rusted loop in the middle of the back. It's a neat recovery. There will probably be more expert buttons people replying and correcting or corroborating my ID.