No expert here, but I would think that sharp edges on the work, or evidence of once-sharp edges, where the leather would have been carved, would be the best hint. Also, I believe that carving would generally have separated the surface of the leather, exposing non-surface leather at least on the side of the cut, if not more. Don't reckon stamping would do that. Obviously, this would be clearest on a floral design, or similar.