http://www.tacticalintelligence.net/blog/pre-assaultive-indicators.htm
Which was the class in a nutshell, basically. I'd like to add that it's part of LEO training to take a "bladed" or "interview" stance with just about everyone you talk to. Nothing personal. It keeps your sidearm out of easy grabbing distance and helps protect your vitals. It also transitions neatly into a Weaver firing stance with a little practice. If you carry a firearm in a holster on your side, it's not a bad idea to practice this.
An important note: where to put your hands.
Don't let your arms hang down by your side, and don't put them in your pockets. It takes too long to react from this position.
Don't put them up by your face like a boxer. It's too aggressive and the last thing you want to do is provoke an attack.
Don't rest one on the butt of your gun for the same reason. Well, that and if you're carrying concealed you've just announced to the world "I have a gun right here!"
DO sort of cup them together at about the level of your solar plexus. It's relatively non-threatening position that makes it easy to either get your hands up to protect your face, or down to reach your gun. This guy has it almost perfect, except he has his fingers interlaced. Maybe it works for him, but most people will squeeze their hands together when startled in this position, and it may take an extra second to pull them apart.
