§ 632. Model Designation Markings.

All devices shall be marked with a model designation which differentiates one model from another unless they are identical except for right- and left-hand mounting, housing finish or material, number and type of bulbs or functions, or number of wiring connections to a switch. Warning lamps of the lightbar type, which are of the same design and construction except for number and type of warning lamp or siren functions, may have the same model number provided they also have a permanently marked serial number either unique to each unit or coded to indicate the particular functions.