Bus. & Prof. Code, § 5365

When a highway within an incorporated area is designated as an interstate or a primary highway, each advertising display maintained adjacent to such highway shall thereupon become subject to all of the provisions of this act. For purposes of applying the provisions of this act, each such display shall be considered as though it had been placed along an interstate or a primary highway during all of the time that it had been in existence. Within 30 days of notification by the director of such highway designation, the owner of each advertising display adjacent to such highway shall notify the director of the location of such display on a form prescribed by the director. The director shall issue a permit for each such advertising display on the basis of the notification from the display owner; provided that such permits will be issued and renewed only if the owner pays the fees required by subdivision (b) of Section 5485. Each permit issued pursuant to this section shall be deemed to be a renewal of an original permit for an existing advertising display.