Some years ago (15, or, more likely, 20) I was looking for stamp pad
ink to work on Kodachrome [remember them?] plastic mounts. There was
some mob in Melbourne that supplied suitable stuff, but it was only
available in one litre (or larger) lots and that was far too expensive
for me when I probably only needed a 50 ml phial to last a couple of
decades! (Assuming coverage similar to standard stamp pad ink.)
Christ knows if it would work in a printer, or even if it's still
available. But that's the best I can offer. IIRC I originally
tracked it down by asking around local printing works. If my old
files weren't already in a deep litter system I might have been more
helpful.
Staedler of Germany markets a 4-pen set of markers that are safe for CDs
and DVDs. They dry rather quickly, and are said not to bother the discs'
layers. They seem to come only with Medium (really thick) points, making
small writing not legible.
Rod is already aware of that sort of implement, as he said above.
As a matter of interest, I've found that some brands of "CD safe" pens
work as you would expect on nearly all types of CDs *except* Verbatim!
I don't know whether they actually damage the upper layer on Verbatim
CDs, but after a period of time they "smudge" badly as they bleed into
the layer. I don't know if this still happens with modern Verbatim
disks because I stopped writing on them when I noticed what was
happening six or eight years ago.
Cheers, Phred.