I guess that all kids at one point or another use banknotes as a drawing paper. Some just do it once to express protest against the mass production or anything else. Others practice bill drawing several times just to establish where is the line between enhancing a banknote and converting a banknote into useless peice of paper.
But I had yet to see any serios art on top of the banknotes. Today – I did. Kamiel Proost has two galleries with pictures: 1 dollar bills and 5 dollar bills. Some Most of them are really amazing!