Hobo Nickels from the early 1900's. The Buffalo Head nickel was particularly popular because of its larger size and carving or engraving surface. Called a Hobo nickel becaus they were more likely to carry coins.
Double sided hobo nickel by George Washington "Bo" Hughes, a black hobo who started carving Buffalo nickels when they came out in 1913 and kept carving them until late 1981 or early 1982 when he disappeared from a hobo jungle in Florida, never to be seen again. This coin recently sold for $24,200