simpson
You could try using paint stripper to remove the old paint or gasket remover(the stuff I get comes in a spraycan). Are you going to repaint the frame? If you just want the tag cleared then mask it off and give that a try. I just would buy a new tag like bwolfie recommended, as they are readily available along with the rivets. It just depends on how deep of a restoration you plan on doing.
Regards,
CNN