The marking is not anything I readily recognize, some sharper photos could assist research efforts.
What I can tell from the photo supplied is that this is applied with a stencil, observing the "splits" in the letters. What does that tell us? Not much aside from the fact that if there was a stencil made it almost certainly wasn't some idle soldier's graffiti and it would have been applied to more than one rifle.
Since it is a likely a simple fixed stencil, and probably not made with easily changed templates, so it should not be a rack number. I think it is a ownership or unit marking, possibly a military, para-military or police unit. Since it is an Ishapore rifle, I would then look to Indian, Pakistan, and other non-western nations.
Time to bust out the google based on those suppositions and see if there are any returns.