California Code, Vehicle Code - VEH § 27904.5

Subject to Section 35783.5, a pilot car shall display neat, clean, and legible signs containing the word “OVERSIZE.”  The words “OVERSIZE LOAD,” “WIDE LOAD,” or “LONG LOAD” may be substituted as applicable.  The sign shall be a minimum of 48 inches above the ground and shall be legible at 45 degrees from either side when read from the front or rear.  The sign shall have a bright yellow background with a minimum projected area of 440 square inches.  The lettering shall be black with a 1-inch minimum brush stroke width and a 6-inch minimum letter height.