Someone has created a collection on the Flickr web site of images paper money sporting graffiti, particularly defaced portraits. It's a kind of folk art in a way, like Hobo nickels without the craftsmanship. "Assassination" is tasteless, but some others are amusing.
Here's Abe Lincoln as Spock from Star Trek. Below are a few examples of the royal treatment of the Queen on Canada's currency.
-Editor