I just cleaned some marker off a copy of King's Knight for the NES. Had "Property of" and the guys name on the back with a #15. Came out perfect! I used a variation of methods that's been mentioned in this thread. I cannot reiterate how well tooth paste works for cleaning things! I took a cotton ball, dabbed a little bit of alcohol on it. Rubbed the hell out of it, and it was SLOWLY coming off, but not fast enough. I then decided to try using some tooth paste in the mix. I rubbed some tooth paste on the writing until it somewhat dried out, THEN proceeded to rub with the cotton ball with alcohol on it. The combination of the alcohol and tooth paste took it right off! I think that might have been a bit quicker than using a tooth brush. Also, I didn't have an electric tooth brush either. So if you have a cotton ball, some alcohol, and a little tooth paste you can take the writing right off! And it didn't mess up the texture of the cart either. The bathroom is my friend..
Anyways, just thought I'd chime in again.