“Lawfully erected” means, in reference to advertising displays, advertising displays which were erected in compliance with state laws and local ordinances in effect at the time of their erection or which were subsequently brought into full compliance with state laws and local ordinances, except that the term does not apply to any advertising display whose use is modified after erection in a manner which causes it to become illegal. There shall be a rebuttable presumption pursuant to Section 606 of the Evidence Code that an advertising display is lawfully erected if it has been in existence for a period of five years or longer without the owner having received written notice during that period from a governmental entity stating that the display was not lawfully erected.