Cal. Veh. Code § 36508

After July 1, 1970, no new implement of husbandry designed or intended by the manufacturer to be operated or moved at a speed not in excess of 25 miles per hour shall be sold in this state unless it is equipped by the manufacturer with a slow-moving vehicle emblem as prescribed by Section 24615, and such an emblem shall thereafter be displayed and maintained on such implement of husbandry while the implement is able to be operated upon a public highway.