A gold color metal and enamel device 1 1/8 inches (2.86 cm) in height overall consisting of a scarlet nonagon, one angle up, bearing a gold radiated disk above and between two gold crosses patty, each cross charged with a gold disk bordered scarlet, all above a black indented base, and overall a vertical white wavy stripe throughout; at the top, surmounted by the nonagon, the gold triple-towered wall from the coat of arms of Manila above and in back of a gold fleur-de-lis on each side, all above a curved scarlet scroll in base inscribed FIRST TO SERVE in gold letters.
Scarlet and white are the colors used for the Corps of Engineers, the original designation of the unit. The triple-towered wall refers to the old walled city of Manila and signifies the historic organizations campaign participation in the Philippine Insurrection. The two fleurs-de-lis represent service in World War I and World War II, and the two crosses with disks denote the two French Croix de Guerre decorations awarded to the unit. The gold radiated disk depicts the sun from the flag of South Dakota, The Sunshine State, and indicates the Groups allotment to the South Dakota Army National Guard. The black peaks in base, which refer to the Black Hills and the wavy stripe for Rapid Creek suggest the Headquarters at Rapid City. Additionally, the vertical stripe alludes to First in the motto, and together with the circular disk of the sun symbol and nine sides of the nonagon indicates the Groups numerical designation (109).
The distinctive unit insignia was originally approved for the 109th Engineer Group on 5 May 1971. It was redesignated effective 1 September 2008, for the 109th Support Group, with the description and symbolism updated.