Cal. Bus. & Prof. Code § 13480

(a) It is unlawful for any person to sell any petroleum product referred to in this chapter at any place where petroleum products are kept or stored for sale, unless there is affixed to each container, receptacle, pump, dispenser, and inlet end of the fill pipe of each underground storage tank, from which or into which that product is drawn or poured out for sale or delivery, a sign or label plainly visible consisting of the name of the product, the brand, trademark, or trade name of the product, and, in the case of engine fuel and kerosene, the grade or brand name designation.

(b) When the product is oil, as defined by Section 13401, each sign or label shall also have in letters or numerals, plainly visible, the viscosity grade classification as determined in accordance with the SAE International latest standard for engine oil viscosity classification SAE J300 or manual transmission and axle lubricants viscosity classification SAE J306, as applicable, and shall be preceded by the letters “SAE.”

(d) When the product is a motor fuel consisting of a mixture or premixture of gasoline and oil or gasoline-oxygenate blend and motor oil, there shall be conspicuously displayed on the dispensing device at least one sign or label stating the ratio of gasoline to motor oil or gasoline-oxygenate blend to motor oil.

(e) All signs or labels required by this section for retail motor fuel dispensers and containers of more than one gallon capacity shall be in letters and numerals not less than one-half inch (12.70 mm) in height. On containers of one gallon or less, the signs or labels shall be in letters and numerals not less than one-fourth inch (6.35 mm) in height and one-sixteenth inch (1.59 mm) in width.