We’ve been asked frequently whether or not this is legal. We can assure you that it is perfectly legal to stamp this message on your bills. The actual law can be found in 18 U.S.C. § 333 which states:
“Whoever mutilates, cuts, defaces, disfigures, or perforates, or unites or cements together, or does any other thing to any bank bill, draft, note, or other evidence of debt issued by any national banking association, or Federal Reserve bank, or the Federal Reserve System, with intent to render such bank bill, draft, note, or other evidence of debt unfit to be reissued shall be fined under this title or imprisoned not more than six months, or both.”
So in order to be charged with this crime, you would have to intent to render the bill unusable. Having this stamp which is semi-transparent, even directly over any numbers or text, does not render it unreadable, and therefore is not unusable. It also still works in vending machines. We’ve tried. We’ve also deposited several thousand all stamped to a bank teller which ran through a counting machine and accepted and deposited into our account.