(a) Lamps that serve two purposes, such as a combination number plate lamp and tail lamp, may be used to satisfy the requirements of this Part.

(b) On omnibuses, an illuminated destination sign on the front of the vehicle, not less than 6 inches high and 24 inches in length and clearly visible for a distance of 500 feet, may serve in place of the identification lamp.

(c) On school omnibuses displaying an illuminated school bus sign, as required by regulations promulgated by the Commissioner of Motor Vehicles with respect to flashing red signal lamps and signs on school omnibuses, such illuminated signs may serve in place of the identification lamps on both the front and rear.