California Code, Streets and Highways Code - SHC § 101.1

(a) The department may place the state's 9-1-1 emergency telephone number on road signs on all state highways at state entry points and county, city, and town limit entry points.  The department shall place and maintain, or cause to be placed and maintained, on all state highways at the city limit of each incorporated city and at the limits of each unincorporated town, as determined by the department, a uniform road sign which sets forth the name of the city or town, its population, and its altitude, as determined by the department.  Where the limits of a county, city, or town intersect a state highway at more than two points, the department, in its discretion, need erect the signs only at each of the two outermost points on the state highway where the intersection occurs.

(b) The department shall adopt specifications to provide for uniform signs of permanent character setting forth the information required in subdivision (a).  The emergency telephone numbers shall be added to the road signs in subdivision (a) only when the signs are changed for other purposes.