California Code, Business and Professions Code - BPC § 5364

The provisions of this article shall apply to any advertising display which was lawfully placed and which was in existence on November 7, 1967, adjacent to an interstate or primary highway and within the limits of an incorporated area, but for which a permit has not heretofore been required.  A permit which is issued pursuant to this section shall be deemed to be a renewal of an original permit for an existing advertising display.