Yes, the "13" at the end of the markings would be tha "rack number" of the revolver within whatever unit the rest of the markings signify ...
If the markings relate to WWI issue, I believe the unit would be the 12th Canadian Machine Gun Company (part of the 2nd Division of the Canadian Machine Gun Corps.) If so, I assume the specific sub-unit within that Company was "G Battery" ...
Alternatively, if they are post-war markings, when the CMGC was reorganized within the National Permanent Active Militia, then the markings would likely denote G Company (or Battery?) of the 12th Machine Gun Battalion, in Saskatchewan from 1919 to 1936.
I am summarizing from the rather convoluted history set out on this page of canadiansoldiers.com:
https://www.canadiansoldiers.com/corpsbranches/machineguncorps.htm