Veh. Code, § 21355

(a) Stop signs erected under Section 21350, 21351, 21352, or 21354 may be erected either at or near the entrance to an intersection.

The Department of Transportation and local authorities in their respective jurisdictions may erect stop signs at any location so as to control traffic within an intersection.

When a required stop is to apply at the entrance to an intersection from a one-way street with a roadway of 30 feet or more in width, stop signs shall be erected both on the left and the right sides of the one-way street at or near the entrance to the intersection.

Notwithstanding any other provision of this code, stop signs shall not be erected at any entrance to an intersection controlled by official traffic control signals, nor at any railroad grade crossing which is controlled by automatic signals, gates, or other train-actuated control devices except where a stop sign may be necessary to control traffic on intersecting highways adjacent to the grade crossing or when a local authority determines, with the approval of the Public Utilities Commission pursuant to Section 21110, that a railroad grade crossing under its jurisdiction presents a danger warranting a stop sign in addition to a train-activated control device.

(b) Notwithstanding subdivision (a), local authorities, with respect to streets under their jurisdiction, are not required to conform lawfully established intersection configurations existing on January 1, 1985, to meet the requirements of subdivision (a) until January 1, 1990.