California Business And Professions Code Section 5408.5

In addition to the advertising displays permitted by Sections 5405 and 5408, advertising displays located on bus passenger shelters or benches and conforming to the following standards may be placed on or adjacent to a highway: (a) The advertising display may not be within 660 feet of and visible from any federal-aid interstate or primary rural highway, and any advertising display within 660 feet of and visible from any urban highway shall be consistent with federal law and regulations. (b) The advertising display shall meet traffic safety standards of the public entity having operational authority over the highway. These standards may include provisions requiring a finding and certification by an appropriate official that the proposed advertising display does not constitute a hazard to traffic. (c) Bus passenger shelters or benches with advertising displays may only be placed at approved passenger loading areas. (d) Bus passenger shelters or benches with advertising displays may only be placed in accordance with a permit or agreement with the public entity having operational authority over the highway adjacent to where, or upon which, the advertising display is to be placed. (e) Any advertising display on bus passenger shelters or benches may not extend beyond the exterior limits of the shelter or bench. (f) There may not be more than two advertising displays on any bus passenger shelter. (g) Advertising displays placed on bus passenger shelters or benches pursuant to a permit or agreement with a local public entity shall not be subject to the state permit requirements specified in Article 6 (commencing with Section 5350).