No sign, device or poster, whether permanent or temporary, whether for advertising
or other purposes, shall be placed or carried on or inside any vehicle regulated by
this article without the approval of the director of the department of safety and
permits. Such sign, device or poster, when approved, shall relate to the business
of transporting passengers for hire on the public streets, and to any products, places,
establishments or other businesses, occupations, persons or subjects, as approved
by this article. In addition, a person licensed under this chapter may affix one sticker
of not more than two inches by three inches in size to the right front wind-vent window
of his certified vehicle, indicating that such owner is a member of a recognized transportation
organization or association composed of persons licensed under this article.
