It looks like something is stuck to the surface. It could be glue or gum. Use a wooden toothpick and try to remove some without damaging the coin. If it is something stuck to the coin, it may flake off. Do you know the weight?
The first US coin motto was found on a 1792 half disme and read: "LIB (erty) PAR (ent) OF SCIENCE & INDUSTRY"