Originally posted by UncleVanya I don’t know what would be unsafe.
Some pens can contain solvents such as Xylene* that can adversely affect the resin that hold the carbon fibers together. Although the resin is formulated to be as inert as possible each manufacturer uses slightly different formulations and additives for Ultraviolet resistance, these variations make using solvent based markers a bit of a minefield. Using tape is by far the safest solution. I use paper medical tape, as it can be written on and is easy to cleanly remove without leaving residue.
* Xylene smells overpoweringly of overripe bananas to me, I get headaches working with the stuff in the lab.