Some say a "Sharpie" can potentially wreck CDs and DVDs by seeping through the disk to the other side, effectively ruining data/files on the CD/DVD. However, I myself have marked more CDs and DVDs then I can count, and none, (that I know of) have suffered any damage due to the Sharpie or permanent felt marker. So, labeling a CD/DVD with a felt marker such as a "Sharpie", I would say is completely fine to do. Completely covering entire CD/DVD in black felt marker from top to bottom? Not so good, maybe?