Cal. Sts. & High. Code § 1970

(a) Local authorities, with respect to highways under their respective jurisdictions, may place and maintain, or cause to be placed and maintained, courtesy signs to recognize the sponsors of the Adopt-A-Riverway Program.
(b) Courtesy signs shall be consistent with existing code provisions and department rules and regulations concerning signs.
(c) Courtesy signs shall only be placed upon the highways of a local authority, upon the approval of an authorizing resolution by a majority of the members of the governing body of that local authority. The resolution authorizing the placement of courtesy signs shall include all of the following:
1. (1) A general plan of where the courtesy signs will be placed within the geographical borders of the local authority, including any street, bike trail, or pedestrian path.
2. (2) A finding that the planned placement of the courtesy signs would not degrade the natural environment of the area.
(d) Courtesy signs shall contain the title “Adopt-A-Riverway” at the top of the sign and the name or logo of the sponsoring person or entity below the “Adopt-A-Riverway” title. Logos shall be provided at the sponsors’ own cost. Both the title and the logo shall be in large enough fonts that are easily read.