Insignia Description
A gold color metal and enamel device 1 1/8 inches (2.86 cm) in height overall consisting of a vertical purple sword with gold blade in front of a vertical white scroll and radiant from base two red lightning flashes all in front of gold rays radiant from base; all enclosed by a circular purple scroll, ends terminating at each side of the blade at the apex, and inscribed “SECURE SERVE STABILIZE” in gold letters.

Symbolism
Purple and white are colors used for Civil Affairs.  The sword together with the white scroll signifies the unit’s military government and civil affairs mission in support of combat and post combat military operations.  The red flashes connote the courageous and efficient service provided by the organization and also the swift dissemination of required public information.  The light rays, indicative of knowledge, refer to the language capabilities and comprehension of legal systems necessary for effective area administration.  The four design elements (the scroll, sword and two flashes) together with the circular scroll, and five parts of the sword (the blade, two quillons of the cross guard, the grip and pommel) allude to the numerical designation of the battalion.

History
The distinctive unit insignia was originally approved for the 405th Civil Affairs Group on 29 May 1969.  The insignia was redesignated, effective 16 September 2005,  for the 405th Civil Affairs Battalion, with description and symbolism updated.

Source: The US Army Institute of Heraldry