The regulation of the placing of advertising displays by this chapter, insofar as such regulation may affect the placing of advertising displays within view of the public highways of this state in unincorporated areas, shall be exclusive of all other regulations for the placing of advertising displays within view of the public highways of this state in unincorporated areas whether fixed by a law of this state or by a political subdivision thereof.
Ca. Bus. and Prof'l. Code § 5270