try rubbing alcohol if that doesn't work put a little amount of laundry soap on it, let it sit over night then get a damp washrag and wash it off; you could also try hairspray, spray some on it, let it sit a couple minutes then wash it off with a damp washrag. if none of those work try to call a dry cleaners and ask them about it.
nail polish removerHow do I clean stainless steel appliances & remove water marks?
nail polish removal could also workremoving marker and fabric paint from walls
if its oil based ur screwed. I have used sharbies on my jeans and never came off or even smugedHow to remove large amounts of hairspray from upholstery?
I've had luck with windex. i dont know why but it works over time XDIron on patches, can you reuse them?
try nail polish remover or hairspray but its easier just to get a new backpack.
How do I remove sharpie from my bike sign on my bag