1980 memorial lincoln cent with either dropped letter (O) or number (0)..was listed as such. the last picture is from original listing, he had a better shot of it than i do in hand.
certainly looks circular, like a digit or letter..look at closeup, the curve, too much of a digit to be just debris, i think..
like i said, it could be a fragment from another coin, but it is not a dropped number. That inclusion is copper, not impacted grease, therefore it cannot be a dropped number.