California Code, Vehicle Code - VEH § 36509

(1) When the vehicle is required to display a “slow moving vehicle” emblem as defined in Section 24615.

(2) When the width, length, height, or speed of the vehicle may cause a hazard to other traffic on the highway.

(1) Flashing amber warning lamps.

(2) Flashing amber turn signals.

(3) During daylight hours, red flags, each of which shall be not less than 16 inches square, mounted at the left and right outer extremities of the vehicle or load whichever has the greater horizontal dimension.