CDRs: do NOT use just anything to write on your discs, you can damage the reflective layer. Sharpies are OK, or use a dedicated CDR marker. Doughnut-shape paper labels are OK but not recommended. Other paper labels are a no-go.
DVDRs: DO use just whatever you like to write on your discs, the reflective layer is under a polycarbonate layer and you cannot damage it with sharpies, permanent markers, you name it.. even a ball pen (though the pressure of a ball pen could be a problem, actually, if you're heavyhanded :bigsmile: ). Paper labels of all sorts are to be avoided, they bring lots of reading issues and can render, in some extreme cases, your discs totally unreadable.