Well in the old days BASF ceramatic coated disc's (TY manufactured) allowed to be abused by allmost everything.
I have used pencils and ballpoints once for labeling which didn't gave any real problems.
Still wonder if Taiyo Yudens that's medai with ceramatic coating has the same quality coating I expect it to be. (*So which european store is smart to start selling these because me and some compannies and some people in the public sector (Read Universities and Hospitals) want these disc's back. The newer EMTEC can not match with the old TY version. )
It was possible with the old basf (made by TY) to remove the whole coating layer which gave you a pure silver disc which was still playable.