Clearance lights and marker lights help identify the size of a vehicle, truck, or trailer. Clearance lamps indicate the overall width and height, and marker, or side marker, lamps indicate the overall length. Combination clearance/marker lamps are available. Truck cab marker or identification lamps serve a similar purpose. Specific requirements, including colors, number, mounting, and performance, are spelled out in FMVSS/CMVSS 108 and state rules. Applicable SAE lamp ID codes are P2, PC, or P3.