Abstract: A method for verifying the authenticity of a sales record, including the steps of: 1) providing a printer ribbon with an ink applied thereto, said ink having a first color and being capable of changing to a second color when acted upon by a reagent; 2) utilizing said printer ribbon to print sales records at the point of sale; and 3) verifying the authenticity of said sales records by exposing said sales records to a reagent capable of causing said ink to change to a second color identifiably distinct from said first color to identify as unauthentic any printing on said sales record not accomplished by said ink. Optionally, the ink used may be oil-based.