T.B.
If it's a dry erase marker, I would just accept that fact that the marker is there. Dry erase markers do NOT come off of anything. Trust me, I've had my share of destroyed things from dry erase markers.
Sharpies might be removed but it could take a lot of work but it's always worth trying. First, try using finger nail polish remover on a Q-tip and rub gently at the stain. If that doesn't work, try straight acetone. IF that doesn't yield any results, try the Mr.Clean Magic eraser. Honestly, I don't think there is anything the Magic eraser won't remove. If nothing works, then search online and see what you find. Good luck!