Hobo Nickels. I love these things.
These were one of the first forms on hobo graffiti. As they were carved into US coinage. Mosty the well known buffalo nickels. Which because of the level of actual nickel content of the coin, were easy to carve into. All these originally looked like this one, with the exception of the date. Buffalo Nickels where minted from 1913 to 1938.