A three-sided channel coupler for connecting the upper and lower portions of a U-shaped sign post, the coupler comprising two U-shaped elements, an outer three-sided, U-shaped element and an inner, three-sided U-shaped element, the three sides of each element comprising a transverse face and two lateral legs, the inner element being smaller than the outer element, a plurality of cross-braces attached to the two lateral legs of each element to hold the two elements together and a plurality of vertical ribs on the inner surface of the outer element and on the outer surface of the inner element.