Any provision of this traffic code to the contrary notwithstanding, all types of signs, signals, and markings, whether in conformity with the standards of the American Association of State Highway Officials, installed by the director of transportation services before April 11, 1967 and in use on the date, for the purpose of regulating, warning, or guiding traffic, are approved and designated as official traffic control devices.
(Sec. 15-6.1, R.O. 1978 (1983 Ed.)) (1990 Code, Ch. 15, Art. 6, § 15-6.1)