California Code, Penal Code - PEN § 2885

No person, firm, partnership, association, or corporation within this State shall sell or offer, trade, consign, keep, expose or display for sale any goods, wares or merchandise manufactured, assembled, produced or mined in whole or in part by the prisoners in any penitentiary, prison, reformatory or other establishment in which prison labor is employed, unless such person, firm, partnership, association or corporation shall keep permanently and conspicuously displayed within the same inclosure and within 10 feet of the place where said prison-made goods, wares or merchandise are kept, exposed, displayed or offered for sale a suitable sign, at least 36 inches wide and 10 inches high, on which appear in legible letters not less than two inches high the following words:  “Convict-made products on sale here.”