Wait... Sharpies aren't considered felt-tip pens?
I've... I've been living a lie....
I'll concede that I'm not 100% sure of that (they do have pretty stiff points), and if the idiot who wrote on the disc pressed too hard, it can cause enough of a disruption in the label side to make the disc unreadable.
The distinction is between a tip made out of matted fiber, and a ball-point pen, or a pen with a plastic tip. Fine line sharpie pens do have plastic tips and should not be used on CDs, but I think normal sharpie pens (the fat ones) are the de facto standard of what you should
be using to write on CDs and DVDs.
Also, HQ professionally made and pressed CDs and DVDs have the layers cemented in the middle, not underneath the silver shiny label.