Probably glue residue. Soak it in acetone for a few hours and see if it lift off. Certainly no error of any type, just PMD.
Fellow enthusiasts nailed it. It may have been stuck to a card at some point...or a school project. It happens quite often.
Just because something looks different, strange or weird does not automatically make it a mint error. There are many ways coins are damaged/altered after they leave the US Mint
I don't think everyone realizes it is not the adhesive spot in the center that you are inquiring about. Lol