Kind thick and heavy for a ramp sight and an iron sight would have a small flat V. That look like some kinda pin with half the circle missing to me.Looks kinda like a mini spike to hold a wire to me. Just guessing.
It is heavy and rusted pretty bad. What kind of sights did the Henry, Sharps and Spencer have? I think they had the flip up leaf sight for the rear. But it still looks like a sight to me unless proved otherwise. The fine V has been rusted out.
it's shaped like a sight, but I don't think it is, the notch just isn't centered. My first thought was maybe a barrel wedge for a muzzle loader double barrel, but that's probably way off.