Here is a picture of the reverse of Wing's bar on his DCM.
It is engraved to represent the Bar to D.C.M. London Gazette 22 August 1918: ‘For distinguished service in the Field, in connection with the campaign in German South West Africa, 1914-15’:- 0134 Sqdn. S.M. F. W. Wing, D.C.M., 5th Mounted Rifles (Imperial Light Horse).