Michigan Compiled Laws, Chapter 257. Motor Vehicles § 257.609

Sec. 609.(1) The state transportation department shall place or require to be placed, and maintain or require to be maintained, upon all state highways traffic control devices as it considers necessary to indicate and carry out the provisions of this chapter or to regulate, warn, or guide traffic.A traffic control device placed and maintained under this subsection shall conform to the most current Michigan manual on uniform traffic control devices.

(2) A local authority shall not place or maintain a traffic control device upon a trunk line highway under the jurisdiction of the state transportation department, except by the latter's permission, or upon a county road without the permission of the county road commission having jurisdiction over that road. With the approval of the state transportation department, the board of county road commissioners of a county, at its option, may install and maintain traffic control devices conforming to the Michigan manual on uniform traffic control devices if the cost would be less than that estimated by the state transportation department and bill the state transportation department for its share of the cost of installation.