Lt. Jim Glennon added a new law enforcement training article on pre-attack indicators to the training section.
If you are not familiar, pre-attack indicators are things someone will say or do that indicate they are preparing to attack you. Jim covers some of the non-verbal indicators in his article. You should definitely read these as they can give you an early warning of an attack.
Anyone that has been on the job longer than a few weeks will likely recognize some or all of these indicators. You should be actively looking for these indicators. When you see them, take immediate action to control the situation and protect yourself.