(a) Automobiles for hire while standing upon any street awaiting employment may display a sign with the words thereon “For Hire”. Such sign shall be of metal and of a uniform size of 6 by 9 inches.
(b) Every vehicle used for carrying passengers for sightseeing purposes while standing upon any street awaiting employment may display a sign with the words thereon “Sightseeing Bus” giving the route, points visited or destination. Sightseeing bus signs shall be of metal of a uniform size of 8 by 24 inches.
(c) The outer surface of all signs specified in this paragraph shall be painted or enamelled a dark color and the letters and figures appearing thereon shall be white.