Strad wrote on Jul 1^st, 2012 at 12:13am:

Would anyone have an idea about the letters on the butt plate? Don't know if they have any corrolation to the SRS records since I need help understanding what they stand for. Thanks, David

They're most likely the initials of someone who once owned the carbine after it was retired from service, since we can imagine any trooper who did that would be be docked a month's pay to buy a new buttplate (not to mention catching a heap of extra duty mucking out stables).