How do I get marker off my backpack?

I got this backpack: http://www.dakine.com/sport-packs/skate/varial/ (if the link doesn't work copy & paste) in Mono Blue. My friends drew on it and it's a really nice backpack. They didn't draw much though. I think they drew on it with an Office Depot Permanent Marker, just like a sharpie I guess. Anyways, how do I get the marker off my backpack?