I believe the factory stamps on the side of the receiver indicate they were manufactured for the military (ie 416, 626 etc). There is a sticky in the red rifles forum that can tell you in greater detail. No factory stamp on the side of the receiver indicates civilian manufacture. Also, obvious variants like the SKS-D and KD are commercial, as well as non-matching serials if I'm not mistaken (someone feel free to correct me if I'm wrong, my memory isn't as good as it used to be.)