The CMF is on these rifles stands for 'Commonwealth Military Forces'.

I too have a rifle with 3.A on the butt along with 10/44 (Which is a stores date and NOT a refurb date.

I've seen a few examples also with 3.A. I looked into it further and I'm of the opinion it stands for '3rd Australianicon Ordnance Depot'. I have a lot more info on this period and why we often see SMLEs with mid-1944 to early 1945 stores dates.