At the time of providing for any decreased or increased maximum speed, the City Traffic Engineer, in conjunction with state highway authorities, shall cause to be posted at either end of such portion of the street, road or highway and at such other points as is deemed advisable, signs of such size as to be easily read, setting forth the maximum speed allowed upon the street, road or highway. Thereafter, it is unlawful for any person to violate any such rule, order or regulation. (Ord. 1477 § 4, 1989: Ord. 304 § 39, 1963).