California Code, Civil Code - CIV § 4710

(a) The governing documents may not prohibit posting or displaying of noncommercial signs, posters, flags, or banners on or in a member's separate interest, except as required for the protection of public health or safety or if the posting or display would violate a local, state, or federal law.

(b) For purposes of this section, a noncommercial sign, poster, flag, or banner may be made of paper, cardboard, cloth, plastic, or fabric, and may be posted or displayed from the yard, window, door, balcony, or outside wall of the separate interest, but may not be made of lights, roofing, siding, paving materials, flora, or balloons, or any other similar building, landscaping, or decorative component, or include the painting of architectural surfaces.

(c) An association may prohibit noncommercial signs and posters that are more than nine square feet in size and noncommercial flags or banners that are more than 15 square feet in size.