S.C. Code Ann. § 56-5-930: Placing and maintaining traffic-control devices on state highways.

The Department of Transportation may place and maintain such traffic-control devices, conforming to its manual and specifications, upon all state highways as it shall deem necessary to indicate and to carry out the provisions of this chapter or to regulate, warn or guide traffic. No local authority shall place or maintain any traffic-control devices upon any state highway without having first obtained the written approval of the Department of Transportation.