War relic or cool rock?

[AlwaysHunting]

Any ideas what this could be? Completely round and smooth minus a rough spot on one side.

 

[hoser]

Possibly a clapper for a bell. First pick looks like a number 8 stamped in the small round spot. ???

 

[BobOso]

It was attached to something, hoser is probably correct for it being a bell clapper.

 

[mudwhale]

That is a Cow Earring. Some lonesome farmers liked to pretty up their animals for certain occasions. It probably fell of during the struggle.
Nice find!