Abstract: A method is provided for automatically printing a unique serial number on MICR documents wherein the serial number may be used to identify the source of the document. If problems occur during subsequent processing of the document, the serial number may be decoded to identify the source of the document for repair, etc., or to identify the source of printing fraudulent checks or if the document was printed on stolen equipment. The unique codes are preferably embedded within character fonts used to print the MICR documents. In this manner, no further modification to MICR printing systems is required. Rather, by modifying MICR fonts to each include a unique serial number, the serial number is automatically printed on all documents printed using the font.