The only way to check is to Jack the rear and spin the wheels.
Put the car in neutral, handbrake off, chock the front wheels, use axle stands at the back or at the most jack the car until the back wheels are only just clear of the ground.
Turn a wheel in either direction. If the wheel on the other side goes in the same direction the diff is an LSD. If it goes in the opposite direction it is a normal diff.
