How do you remove marks from UR Dr Who cards?

I have several Dr Who Ultra Rare cards that I was thinking of selling, but they appear to have what looks like permanent marker (although may be just dirt or something else) on them.

I don't want to try rubbing them with various liquids incase the design comes off, but if anyone knows of something that will work (for instance, baby wipes?), then suggestions are more than welcome!

Many thanks,