Ohio Rev. Code § 4511.10: Placement and maintenance of traffic control devices.

The department of transportation may place and maintain traffic control devices, conforming to its manual and specifications, upon all state highways as are necessary to indicate and to carry out sections 4511.01 to 4511.78 and 4511.99 of the Revised Code, or to regulate, warn, or guide traffic.

No local authority shall place or maintain any traffic control device upon any highway under the jurisdiction of the department except by permission of the director of transportation.