as marines542 said, overheating can be a sign, but often, you can tell before it gets that hot. If youre cruising and your car is running a few degrees higher than yesterday, or if it takes longer for the gauge to drop once the stat opens or the fan kicks in, that can be a sign.
I drove for most of the summer with the pump on the way out, i noticed the car was running closer to 210 than the usual 188-192 but i figured it was because it was over 80 outside. The day before it failed it had been running 215-220. When it finally went, i had steam, no power (because the belt got wet and was not running the alternator or p/s pump), and it got up to 230 and the heat was blowing cool. I made it into a Wendys parking lot and shut er off before it reached the red zone.
I watch the temperature like a hawk. Thats why I dont understand some of these new eco-box cars dont have a gauge, just an idiot light. If its 65 outside and at speed you normally run at 190 (give or take ten degrees) and it seems like youre staying closer to 200-205, thats your early warning that something is amiss. Granted 205 is not outside the normal range, when you know your car, you know when she's not feeling well.