R.I. Gen. Laws § 31-13-2: Devices on state highways.

(a) The state traffic commission shall place and maintain any traffic control devices, conforming to its manual and specifications, upon any state highways, that it shall deem necessary to indicate and to carry out the provisions of chapters 12 — 27 of this title or to regulate, warn, or guide traffic.

(b) No local authority shall place or maintain any traffic control device upon any highway under the jurisdiction of the state traffic commission except by the latter’s permission.