California Code, Business and Professions Code - BPC § 7050

(a) This chapter does not apply to an artist who draws, paints, applies, executes, restores, or conserves a mural pursuant to an agreement with a person who could legally authorize the work.

(b) For purposes of this section, ”  1mural” means a unique work of fine art that is protected by copyright, trademark, label, or patent and that is drawn or painted by hand directly onto interior or exterior walls or ceilings, fixtures, or other appurtenances of a building or structure.  “Mural” does not include painted wall signs.