The purpose of this section shall be to coordinate the type, placement and scale of signs within different land use zones; to recognize the communication requirements of all sectors of the community; to encourage the innovative use of design; to promote both renovation and proper maintenance; to protect public safety; to allow for special circumstances; and to guarantee equal treatment under the law. These shall be accomplished by regulation of the display, erection, use and maintenance of signs. The use of signs is regulated according to zone. The placement and scale of signs are regulated primarily by type and length of street frontage, and surrounding conditions must also be considered. All signs hereafter erected or maintained, except official traffic and street signs, shall conform with the provisions of this chapter. Any signs not specifically permitted are prohibited.