I’ve never come across these before, but reading this months Smiths Journal, there’s an article about the art form known as hobo nickels. Pretty damn cool!
Some info - Hobo nickel - Wikipedia
Some photos - https://www.google.com/search?q=hobo+nickel&tbm=isch
Well I have never seen or heard of them but I think they are bloody marvelarse and now I want to collect them! Some of them are extremely well done.
The trouble here is I now want to try it myself and asking myself - “Should I sacrifice a 1921 American silver dollar I have here”
Yeah, practice on the silver but keep the gold sovereigns till you get good 
Some examples taken to the next level, particularly like the booby trapped one…