Disclosed is a protected document such as a negotiable instrument, a title instrument, identification document or other documents which should be kept secure from illegal copying by color copiers. The method of making the document comprising preprinting a "VOID" or other warning or cancellation phrase...http://www.google.de/patents/US4210346?utm_source=gb-gplus-sharePatent US4210346 - Protected document bearing watermark and method of making
