How shall I clean it. Can it be done without harming the digitizer? How sensitive is it on the inside of the glass?
With the lack of response I chose to use wipes and cleaning solution from a Dust-Aid kit for cleaning DSLR sensors. I believe the cleaning agent is heptan, but it doesn't say on the bottle, so I can't be sure.
Anyway. It worked well. Had to rub a bit to get the ink off, but with a little patients it rubbed off without leaving any residue. Now the only defect in the glass is a small scratch. (which may well be why there was ink markings there. Probably a production flaw and the reason I got the digitizer cheap on ebay. Anyway it won't bother me much. Certainly not enough to replace the glass again.