A sensor for sensing and identifying characteristics of a printer ink ribbon when a ribbon supply roll is inserted into a printer and operated. Ink ribbon cartridges used in printers are provided in a number of types, colors, and other identifiable characteristics that are important for insuring that the correct ribbon is inserted in the printer for the then current print job. In the present invention, the ribbon cartridges include ribbon supply rolls which are provided with identifying indicia on one end of the roll, and a sensor to read the presence of indicia when the printer is operated. The positions of the indicia relative to selected reference positions indicates the ink ribbon type. Suitable circuitry is used to disable the printer if the print ribbon is not properly correlated to the requirements of the printer. A Hall Effect Sensor is used adjacent the print roll, and the indicia on the ink ribbon roll comprise pins or similar members that will affect the Hall Effect Sensor output when rotated past the sensor.