Most obviouse sign is when you let it out and the car don't go .....
..... but if ever it slips when you just go WOT in 4th or 5th gear, then it's on it's way out!
I'll second that. Plus, when you push it to the floor and it won't go into gear. When you smell burning clutch. When you push on the gas and it slips! If you don't have any signs, don't change it.