In an effort to present the aid to South Vietnam as an alliance of many flags, US troops were permitted to wear the Free World Military Assistance Forces (FWMAF) detachable patch on the left pocket of their khaki uniform1. However, though this was authorized by MACV in late 1966, the FWMAF pocket hanger was rarely worn.2
1. Pocket hangers enabled unit insignia to be displayed when wearing the summer tan / khaki uniform and were suspended from the right pocket flap button.
2. U.S. Army Uniforms of the Vietnam War by Shelby Stanton (Stackpole Books 1992)