A mounting bracket assembly for supporting a traffic control device on a mast arm or pole. The bracket includes a first clamp adapted to removably attach to the mast arm or pole or other elongate support, and is designed to be positioned vertically or horizontally. A second clamp is removably attachable to pole or other elongate support member supporting the traffic control device. The second clamp includes inner and outer clamp members. The inner member has a pair of arcuate slots that are alignable with either of two pairs of bolt holes in the first clamp. Thus, the arcuate slots in the inner clamp member and the first and second pairs of bolt holes in the first clamp permit rotation of the inner clamp member 360 degrees relative to the first clamp.