"General Macarthur, C.M.G., D.S.O."
C. M. G. stands for "Companion of the Order of St. Michael and St. George
." The Order was created by the Prince Regent (later King George IV) on 27 April 1818 to commemorate the British protectorate of the Ionian Islands. It is awarded for non-military service abroad, and for service in the Foreign and Commonwealth Office.
D. S. O. stands for "Distinguished Service Order," a British military decoration awarded for gallantry during war.