(a) Nonrestricted vehicles, except taxicabs and vehicles owned and operated by governmental agencies, having any name, insignia or sign painted or displayed thereon are prohibited within the parkway system, except for identification purposes.

(b) For purposes of identification, the name and address only of the owner of a nonrestricted vehicle appearing on the sides thereof in letters not more than two inches in height shall not be construed as being in violation of this Subchapter.