Those are standard Arabic numerals, as used by Turkey at that time; Iranian (Farsi) numbers are different in the 4, 5, and 6. Nothing is upside down.
The original rifling in the Model 88 had a bore diameter of .311"*, with a groove diameter of .318". But that left a land height of only .0035", not enough to resist the corrosive primers and erosive powders of the day. So, after the adoption of the Gew. 1898, the Germans adopted new rifling, with a groove diameter of .323", or a land height of .006", more than enough to stabilize bullets even after considerable wear. (The U.S. .30 caliber has a groove depth of .004", with a groove diameter of .308" - hence the designation of some .30 caliber cartridges as ".308".)
The new Model 1898's were recalled and rebarrelled, but the obsolescent Model 1888's were to be issued only to reserves, so they weren't rebarrelled. Instead, the new reamers were run into the chamber to expand the chamber neck and allow expansion of the cartridge neck. That was enough to keep pressures within the safety range. The modified rifles were marked with an "S" on the chamber, and were converted to use the new Model 98 "stripper" clip instead of the old Model 1888 en-bloc clip. Both converted and unconverted Model 1888 rifles served German reserve units through WWI.
Ammunition confusion did not occur, since the en-bloc clips would not fit the converted rifles, and the the new clips would not fit the unconverted rifles.
After WWI, Germany sold a million or so of those converted M1888 rifles to Turkey, along with hundreds of thousands of Kar. 98 (Kar. 98AZ) rifles which became so associated with Turkey that they are often called "Turkish small ring Mausers", even though Turkey never made any Mauser actions.
*English measurements used to avoid confusion.
Jim