Jack up and support the rear of the car. Take one wheel, turn it and observe the other rear wheel. If the other rear wheel turns in the opposite direction, no LSD. If it turns in the same direction, LSD. I'm not sure what you mean by the "good" LSD? There is an "S" stamped on the LSD differential. But it is on the top of the unit, almost impossible to see, unless the unit is out of the car.
What year, model, options, do you have?
1995 325I, window tint, K&N, debaffled airbox, BMW #104 wheels, Nighthawk low beams, smoked side markers, smoked corners, smoked taillights, M3 stlye heated mirrors, various interior bits, Bosal cat-back.