Unit markings are not my thing, but it probably identifies the 212 Reserve Inf. Regt., which was part of the 45th RID, served in Belgium in 1915. I assume it is an authentic unit marking because of its appearance and composition, which during the war was very "individualistic" and rather chaotic compared to pre-war unit markings. Typically the known wartime unit markings are either specialized units or seem to have been done for unique situations. Some coastal defense units and in many cases elite formations seem to have applied unit markings. It is rare on G98's, most known are 98a's or bayonets. Often the unit markings are next to indecipherable, just a series of numbers that can mean anything..
Anyway, Jeff Noll, Wolfgang or a few others that specialize in unit markings could undoubtedly decipher this for you. Perhaps they will when they come for a visit. Some of our other German friends also very skilled with unit markings.
Regarding the rifle, I have this rifle recorded from a 2008 sale, on Gunbroker, didn't save the text though. The pictures were even worse than these though, so little purpose to posting them. The only thing of note was this rifle has been cleaned up considerably, it was pretty rough in 2008. No sling then either, but the clean up looks pretty respectable considering the earlier state.
