Max,

Where did the "GR" appear and on what uniform? Was it the one most people know best, the red serge (the dress uniform with the red jacket) or was it the working uniform (standard police look - greyish shirt, black gun belt)? You are right that it should be bilingual. A thought struck me though, perhaps it is latin? Our coins have D.G. Regina for Dea Gratia Regina (Latin is not my forte so apologies for any misspelling) or, in English, by the grace of God queen. Perhaps it could be George Rex in honour of the sovereign when their name was changed from the Royal Northwest Mounted Police to the Royal Canadian Mounted Police in 1920.