California Code, Public Utilities Code - PUC § 7601

Except as provided in Section 7602 every common carrier by railroad operating within this State shall maintain, on what is known as passing track sidings, a signboard in connection with each derailing switch or other derailing device, whether the derailer is operated where located or from a distance. The signboard shall be placed within 100 feet of the derailer and shall be constructed in either of two forms, viz: board five feet high and 10 inches wide, or sign constructed of two parts, one of which is an upright and the other a transverse board, the upright to be of sufficient height to securely fasten at the top thereof the transverse board, which shall be not less than two feet three inches long and seven inches wide and placed in such a manner that the upper side of the transverse board is not less than four feet above the ties. The board shall have painted thereon the word “derail” in large black letters on a white background.

The commission shall enforce this section.