nS stands for New School. 'Tis an abbreviation for New School.
The lowercase-then-uppercase type is a way of making it look cooler. "nS" originated from Nitto 1320 Challenge, where taking after the team OldSchoolRacing, NewSchoolRacing was created, for the reason in that most racers on the game were not the ones that played around the time of OSR or OldSchoolRacing, therefore NewSchool. nS is painted on the cars, and looks very attractive.
50 Cent is nS.
50 Cent is New School.
I just got on to NewSchoolRacing, and threw the nS up on my Viper.