A piece of scrip is engraved or printed with groups of patterns which can be sensed by a validator for scrip and one of those groups of patterns will define a code which will permit that piece of scrip to be accepted only by a scrip validator or by scrip validators which have that same code stored therein....http://www.google.fr/patents/US3937926?utm_source=gb-gplus-shareBrevet US3937926 - Validator for scrip
