(a) Each passenger motor vehicle subject to this standard must have an identifying number affixed or inscribed on each of the parts specified in paragraphs (a)(1) through (a)(18) inclusive, if the part is present on the passenger motor vehicle. In the case of passenger motor vehicles not originally manufactured to comply with applicable U.S. vehicle safety and bumper standards, each such motor vehicle subject to this standard must have an identifying number inscribed in a manner which conforms to paragraph (d)(2) of this section, on each of the parts specified in paragraphs (a)(1) through (a)(18), inclusive, if the part is present on the motor vehicle.