The (perhaps small) risk with anything stuck on to the card, be that label tape or paper label, is that if, during operation, when the camera + card may become quite warm, the glue 'fails', you may end up with a loose label in the memory card slot (when card removed) which then gets into the connector when you re-insert the next card
Personally I would have suggested the 'permanent' OverHead (projector) pen idea as Giacomo did.
Or perhaps
very gently scoring/engraving the non label side of the card with a sharp pointy tool or needle. (take care - we don't want any 'skewered' finger tips)
btw - good thread title Charles