Grayson, B. and Stein, M.I. (1981) Attracting Assault: Victims' Nonverbal Cues. Journal of Communication 31 (1): 68-75.

This is probably the article I'm referring to. Unfortunately, even though it hit the popular press back in the 80s (that's how I heard of it), I can't find anything but the abstract online.

However, there's a more recent study which didn't use actual muggers, but which found somewhat similar results:

Consistent prototypes of easy and difficult to attack walkers could be identified from each experiment. The prototypical hard to attack walker was characterized by a longer stride length, swinging foot movement, a larger range of arm swing, higher energy, lower constraint, a faster walk, and a relatively heavier body weight than easy to attack walkers. They also moved posturally, with a three-dimensional weight shift, whereas easy to attack walkers moved gesturally, and with a predominantly lateral or forward/ back weight shift. The prototypes identified in our studies are similar to those identified by Grayson and Stein (1981) but were developed using a rigorous methodology that isolated the contribution of kinematic information to perceptions of vulnerability. The characteristics associated with low vulnerability suggest faster escape from potential attack (longer stride length, faster walk, higher energy) or greater ability to defend oneself (heavier body weight; higher energy).

Definition from the article: (postural motion activating the whole body or gestural motion activating only a part of the body)