Sneakylong
Acetone (nail polish remover) should be safe. Just dip a folded up paper towel in it and swipe softly. It should come right off.
"Stains on Marble
Pens or markers left uncapped may leak onto your marble surface as well. If the spill goes undetected and results in a stain, you may be able to remove the stain by gently applying acetone to the stain with a soft cloth. The Marble Institute of America recommends only using acetone on dark stones."
