The driver of any vehicle shall obey the instructions of any applicable official traffic-control device unless otherwise directed by a police officer, subject to the exceptions granted by this chapter to the driver of an authorized emergency vehicle; provided, that no provision of this chapter for which signs are required shall be enforced against an alleged violator if at the time and place of the alleged violation an authorized sign is not in proper place and sufficiently legible to be seen by an ordinarily observant person. Whenever a particular section does not state that signs are required, such section shall be effective without signs being placed to give notice thereof.
(1991 Code, § 70.20) Penalty, see § 70.99