Whenever by this chapter or any other section of this code any parking time limit is imposed or parking is prohibited on designated streets or portions of streets, it shall be the duty of the city engineer to erect or cause to be erected appropriate signs giving notice thereof and no such regulations shall be effective unless signs are erected and in place at the time of any alleged offense. When the signs are so erected giving notice thereof, no person shall disobey the restrictions stated on such signs. (1985 Code §2.1-2.1024)