(A) No provision of this code for which official traffic-control devices are required shall be enforced if, at the time and place of the alleged violation, an official device is not in proper position and sufficiently legible to be seen by an ordinarily observant person. Whenever a particular section does not state that official traffic-control devices are required, the section shall be effective even though no devices are in place.
(`81 Code, § 14-71)
(B) Whenever official traffic-control devices are placed in positions approximately conforming to the requirements of this section, the devices shall be presumed to have been so placed by the official act or direction of lawful authority, and shall be presumed to comply with the requirements of this section, unless the contrary shall be established by competent evidence.
(`81 Code, § 14-73)