I'd heard of flax-script, hempscript and JSG Boggs*, but until today, I'd never heard of Hobo Nickels.
People have been altering coins for ages, but the Hobo Nickel saw its heyday during the
Great Depression of the 1930s, when hobos would carve hobo faces, trains and other things onto Indian Head Nickels and use them to buy food, lodging and other things.
The Hobo Nickel is still around, but made mostly by artists and enthusiasts. The pirate nickel above is an example of a recent work.
Not only would I love to get my hands on a few genuine Hobo Nickels (ones made by real hobos); I'd also love to learn how to carve my own using the same methods.
Here's another essay on the history of Hobo Nickels.
About.com's entry on Hobo Nickels.
*Example of a banknote drawn by JSG Boggs
