if box is still in the car jack front up with both wheels off ground and spin one of the wheels by hand.if the other wheel turns on the other side at same time then it is a lsd box,if the other wheel doesnt turn its not.

if the box is out, look thru the hole where driveshaft goes in.if it is just a hole then its lsd if u can see a bar goin stait across the hole its not an lsd mate