All traffic-control signals, signs and traffic-control devices to be erected or maintained upon any city street designated as forming a part of the route of a primary state highway or secondary state highway must be approved by the State Highway Commission prior to their installation; provided, however, in cities having a population in excess of 15,000 according to the latest federal census, traffic-control signals, signs and traffic-control devices are subject to approval of the State Highway Commission for installation and type only. All signs and signals required under this chapter for a particular purpose shall so far as practicable be uniform as to type and location throughout the city. All traffic-control devices so erected and not inconsistent with the provisions of state law or this chapter shall be official traffic-control devices. (Ord. 5212 § 1 (Exh. E), 1999; 1957 code § 9.04.090.)