3.10) Is it illegal to use U.S. paper money on products or in advertising?

  Photographs of notes, or portions of notes may not be used in any
form of advertising. The regulations permit their use only for
educational purposes. This regulation is currently being violated
by a number of major TV networks, computer magazine publishers,
telephone card manufacturers  and others. Watch for a Secret Service
crackdown before long on this.  Key chains, watch fobs, calculators,
and other products carrying paper money designs are subject to
confiscation by the Secret Service. This probably also applies to
telephone cards.