Insignia Description
A gold color metal and enamel device 1 3/16 inches (3.02 cm) in height overall consisting of a sword pointed up with gold hilt and white blade between two orange lightning flashes originating at the sword's pommel and terminating on either side of its point; all entwined by an S-shaped gold scroll with that portion extending from upper left to lower right bearing the inscription "EDGE OF THE SWORD" in black letters.

Symbolism
White and orange are the colors of the Signal Corps.  The flashes flanking the sword represent the Signal function in support of the military mission.  The motto is indicative of the spirit of the organization.

History
The distinctive unit insignia was originally approved for the 21st Signal Group on 19 August 1968. It was redesignated effective 16 October 2003, with description updated, for the 21st Signal Brigade.

Source: The US Army Institute of Heraldry