Abstract: The disclosed illuminant display device is to be used on a motor vehicle for publicity or other purposes. In the device an opaque plate member contains perforations in the shape of a character or figure to be displayed, and tinted translucent pieces are set in the perforations transmit light which is projected from a light source provided behind the perforated plate. The display device can serve as an illuminant license plate which is arranged to illuminate the identifying characters continuously for a predetermined time period after the headlight or parking light of the motor vehicle has been turned off and thereby foil a driver who tries to conceal the identity of the vehicle by turning off the lights for hit-and-run or other unlawful purposes.