Lead seal probably from an electric meter.
Cliff
Now that I looked at it closer it is a lead head from a roofing nail.It might have some ridges inside at the bottom, where you would screw it in somewhere.
I'm sure it's a nail head. You can see where the nail pulled out of the bottom.if its not a roofing nail head it is a old toothpast or other tube like cap. I have found several similar.