California Code, Business and Professions Code - BPC § 5494

(a) All on-premises advertising displays which become nonconforming as a result of any such ordinance or regulation are presumed illegal once the amortization period provided by the ordinance or regulation rendering them nonconforming has lapsed and conformance has not been accomplished.

(b) If property containing on-premises advertising displays is annexed to a city or county which introduced or adopted, prior to March 12, 1983, an ordinance regulating on-premises advertising displays, the city or county may apply its ordinance or regulation to the annexed property, and the display shall be deemed illegal upon expiration of any applicable amortization provided by such ordinance or regulation. The amortization period is deemed to commence in such event upon the date of annexation.

(c) When amortization has not been provided in any applicable preexisting ordinance, annexed nonconforming displays ordered to conform to ordinances or regulations of any city or county shall be subject to the requirements of Section 5491.

(d) Amendments or modifications to ordinances or regulations of any city or county adopted prior to March 12, 1983, including amendments which require removal of additional displays or displays which had previously been made conforming, shall be subject to the requirements of Section 5491 if such amendment or modification makes the ordinance being amended or modified more restrictive or prohibitive.

(e) Ordinances or regulations of any city or county introduced or adopted prior to March 12, 1983, which have terminated or will terminate, may be reenacted and are not subject to Section 5491 if reenacted within 12 months of their termination, and if upon reenactment they are not made more restrictive or prohibitive than the preexisting ordinance or regulation.