"Pfister" is likely another piece of adult humour by Rockstar, as its pronunciation is similar to "fister", thus alluding to the sexual practice of fisting.
The name could also be a reference to a similarly-named American pharmaceutical multinational corporation, Pfizer.
In GTA San Andreas, pedestrians in areas like Paradiso and San Fierro can be heard saying what sounds like, "Have you driven a Pfister?" Sometimes, if the player is driving an expensive-looking vehicle, a pedestrian might comment positively, "Is that a Pfister?" This could mean the brand was planned to be introduced before GTA IV with the scrapped system of vehicle brands (as seen in carcols.dat).