Cal. Health & Safety Code § 18092

(a) Every manufactured home, mobilehome, commercial coach, truck camper, or floating home subject to registration shall be issued a registration decal. The design of the decal shall be determined by the director and the decal shall be issued by the department. The decal shall be at least 2 1/2 inches high and 2 1/2 inches wide.
(b) The decals shall be applied to the outside of the mobilehome or commercial coach in a location within 15 inches of the lower front right-hand side which is clearly visible and these decals shall be maintained in a condition so as to be clearly legible. The decals shall be applied to the lower rear left-hand side of the truck camper.
For a floating home, the decal shall be applied in an area six inches from the main entry door on the side opposite the hinged side of the door at a point not less than two feet from either the top or bottom of the door and on the outside surface.
(c) The director, after consultation with county assessors, shall prescribe a registration decal for manufactured homes and mobilehomes subject to registration which clearly indicates, by color or otherwise, whether or not the manufactured home or mobilehome is subject to annual registration with the department or is subject to local property taxation.