this has confused me as well according to all the paperwork for my bike i have a 748 bip but the sticker on the frame says 748 s ??? (it's got showa forks and shock but 3 spoke not 5 spoke wheels )
The "real" S models were made from 2000 onwards, so don't go by what your frame sticker says.
The easiest way to tell is by the components it's got, as Lee says:
5 Spoke Grey Marchesinis Grey Frame Adjustable Steering Angle Showa Shock and TiN Front Forks
It was available in Red, Yellow and the limited edition "S" only grey, like Lee's.
Year 2000 bikes (like mine) didn't have S on the fairing, but the later ones did. This is the same point that the "Bip" became the "E" to make the range E, S and R.
Here's an old picture of mine, in nearly standard form...