Question 93: Is it illegal to deface money?
Answer: There is no law or statute against simply writing on a cash bill. For instance, it is not against the law to draw giant red lips on George Washington's portrait on the front of a One Dollar Bill.
However defacing currency with the intent to alter the bill to gain a benefit is illegal. If someone alters a written instrument (such as a check) without permission and with the intent to gain a benefit, then it is called forgery, which is a crime. If one tried to alter a cash bill (like changing a $5 bill to a $20 bill) for the purpose of presenting the altered bill to gain a benefit, then that could be considered a forgery. Forgery of United States Currency in this manner is called counterfeiting and carries with it very stiff penalties.