Whenever any city or county, by ordinance or resolution, permits, restricts, or prohibits the use of public or private highways pursuant to this article, any traffic control device erected by it on or after January 1, 1981, shall conform to the uniform standards and specifications adopted by the Department of Transportation pursuant to Section 21400.
Source:
Section 21100.1, https://leginfo.legislature.ca.gov/faces/codes_displaySection.xhtml?lawCode=VEH§ionNum=21100.1..