There are several things that I have seen. I have noticed some things in myself and have seen some things in others.
You know how on the news you hear about some guy who goes on a shooting spree and kills a bunch of people at work or whatever? And someone interviewed always seems to say, "he had no expression at all...just a blank stare." I have had that stare myself. That is RESOLVE. When a guy has resigned himself to the fact that he IS going to do this (kill you, punch you, whatever)..there is no more stuggling emotions...just resolve. He is resigned to the task and is not willing to and not going to back down.
I cannot tell you what to look for in someone's eyes before every time they strike, but before they attack in general, there is usually an intense, animal like (I don't like to say "wild" because people think "crazy" and not "animal like")look..that I have seen. In the fights I've been in or seen there are two things that stand out to me.
If his eyes change and he looks more animal like, very intense (you'll know when you see it), he is going to attack.
If he looks relaxed and blank (that "no expression" look), he is planning on killing you.
The blank stare is BY FAR more scary to me than the intense "animal" look...the blank stare means the guy has resigned himself to get rid of you.
The reason that I know this is that I have experienced it myself. I was prevented from killing him by other people who interviened, but I had planned on killing him. Not murder...but self-defense to the ultimate end. In other words, I was not attempting pre-meditated murder...I honestly believed that the only way I could stop this guy was to kill him so I resigned myself to that and went forward.
I thank God that other people got involved and stopped the fight. It was a very serious, real fight.
It's very scary...to me.

As far as how to detect telegraphed moves, you have plenty of opinions in here already. I just know that if someone is going to attack, you can see a certain serious, intense, almost animal look (like something you'd see in the eyes of a snarling dog).

Incidentally, not to sound brutal, but even though we train for self "defense", action is much faster than reaction. If you detect "the look", then you know he is going to attack...I would strongly recommend attacking first. Don't wait. You might not get a chance to (block, strike, move, whatever...) work your mojo.
If he gives you the look, ruin him...and do it quick! There are way too many fights that I WISH I had struck first. By not doing so, I sacrificed the element of surprise, postition, targets, etc.
I think that battle is 90% mind anyway...the look comes from his mindset. If you get the look, consider it an "act of war" and jump in first.

That's my 10 cents

[This message has been edited by totallyfrozen (edited 08-08-2000).]