Every so often your pliers will slip on wire or jump rings and leave marks. If the marks are made by the pliers sliding along the wire or rings and they haven't dug into the metal they can be polished away with either a tumbler, a cloth impregnated with a polishing compound like rouge, or the buffing side of a nail board.
If the tool has dug into the metal, polishing it will just make the marks more obvious. For small scratches sanding with a nail board or fine sandpaper before polishing will erase most marks. These 2 photos are of a 4mm jump ring with tools marks and then after it has been sanded.