The police chief, subject to any directions which the city commission may give by motion or resolution, shall have placed and maintained traffic control signs, signals and devices when and as required under the traffic ordinances of this city to make effective the provisions of the ordinances, and may have placed and maintained such additional traffic control signs, signals and devices as he may deem necessary to regulate traffic under the traffic ordinances of this city or under state law, or to guide or warn traffic. (2001 Code § 70.045)