Knights and Dames Grand Cross use the post-nominal `` GCMG '' . Knights Commanders and Dames Commanders use `` KCMG '' and `` DCMG '' respectively . Knights and Dames Grand Cross use the post-nominal `` GCMG '' ; Knights Commanders and Dames Commanders use `` KCMG '' and `` DCMG '' respectively ; Companions use `` CMG '' .