Misprint Overinked Green Smear
The pictured misprint below has too much green ink. An extra amount of green ink was left on the paper during the printing process. That green ink was then smeared across the back of the note. Extra green ink most often affects the back of the note or the green areas on the front of the bill like the serial number and green seal.
Most of these misprints are fairly common; and even worse, they are easy to fake.
Send us a picture of your misprint and we can make an offer for it. firstname.lastname@example.org