Anastassia Blechko at in-mind.org discusses efforts by psychologists and police agencies to judge intentions based on facial and bodily cues.
Here is Blechko on how U.S. Secret Service agents try to assess whether an individual is armed:
While observing a potential suspect the suspect’s ‘strong’ side is first identified (e.g. by observing which hand or arm a person usually uses for most actions, such as lightning cigarettes, holding, moving objects, or showing something to someone). Once the dominant side of the body is determined, the next step is to look at places on the suspect’s body where a gun can be hidden. The two most common places to hide a gun are the right front waistband and the small pocket of the back. The observation of arm movements, which reveal certain emotions one can experience while he/she is carrying a gun, can predict that someone is hiding a gun. Because the gun is a loose object, the suspects are constantly in fear it will slip, which makes them periodically touch it, consciously and unconsciously, to be sure it’s still there. The way that criminals with concealed weapons walk may also have peculiar characteristics. These characteristics are particularly noticeable when armed subjects are running or moving abruptly. Then they tend to hold the arm against the concealed weapon, either stiffly or with a very restrained swing. Another visual sign associated with walking with a concealed gun is that the stride on the side of the body holding the gun will be shorter than that on the other side. The arm may be held against the gun as a form of protective movement, especially if other people come closer to the suspect.