Police and crooks can spot them instantly. Some people, they'll tell you, look like easy victims.

Granted, there are those who practically send out invitations to assault -- walking down a dark alley alone or flashing a wad of bills in a bus station.

But, other "easy marks" seem to give off subtle signals that ask for trouble. "It's like they're surrounded," says one policeman, "by an aura of muggability."

Ask crime experts to pinpoint exactly what makes someone look "muggable," however, and they'll talk about a "sixth sense I have" or "vibes I get" or admit "I can't define it, but I know it when I see it."

Communications expert Betty Grayson wasn't satisfied with these vague answers. "I was teaching a behavioral science course to a group of police officers," recalls Grayson, a professor at Hofstra University in New York, "and we were talking about the ways people can communicate without words.

"Two cops who worked in plainclothes on the West Side (of Manhattan) told me how they'd spot someone who looked like a victim, follow the person, and sure enough, very often that person would be assaulted."

When the officers could only point to "experience" as the reason they chose the likely victims, Grayson decided to devote her doctoral thesis to "just what kind of nonverbal communication was going on."

Using a hidden camera, she videotaped pedestrians on three successive weekdays between 10 a.m. and noon. She taped each person for about 7 seconds -- the time it takes, she figured, to size up a stranger.

From videotapes of more than 100 people, she selected 60 that fell into one of four categories -- men over 45, men under 35, women over 45 and women under 35. Then she took her tapes to Rahway State Penitentiary in New Jersey -- the prison made famous for its "Scared Straight" program -- and ran them for a dozen inmates who had been convicted of crimes ranging from robbery to murder.

These prisoners' comments about how "muggable" each person appeared became the basis for the following 10-point "assault potential" scale:

1. "Most assaultable, a very easy rip-off."

2. "An easy dude to con."

3. "You could take that one out."

4. "Looks like a fairly easy hit."

5. "You could stand a problem."

6. "Could give you a little static."

7. "Would be a problem, could give you a hard time."

8. "A hard dude to knock off, wouldn't mess with him."

9. "Would be heavy, would give you a hard time."

10. "Would avoid it, too big a situation, too heavy."

Grayson then showed the tapes to a second group of nearly 60 prisoners, who were convicted of assault on persons unknown to them, and asked them to rate each person according to the scale.

"More than half of them," she says, "agreed on rating about 20 of the people as potential easy victims -- either a 1, 2, or a 3.

"Although women in the '45 and older' group were nearly twice as likely to be judged easy victims, an equal number of men and women in the '35 and under' group were picked as easy targets."

Grayson assembled the tapes of those selected as "most assaultable" and had a trained dance analyst evaluate each person's use of 26 different movements that are the basis of Labanalysis -- a dance notation technique used to define and record movement.

"Five movement characteristics were common to all the victims," Grayson notes. "First was the way they lifted their feet. Instead of walking from heel to toe they picked up their whole foot and put it down -- like a Spanish dancer.

"They all used exaggerated strides -- either too long or too short. And they moved laterally. Instead of swinging their right arm with their left leg, they moved the same arm as leg.

"Then there was the way the top of their body moved in conjunction with the bottom of their body. It was like their torsos moved at cross-purposes, with the right shoulder moving in conjunction with their left hip.

"And they walked so that their arm and leg movements appeared to come from outside of their body instead of from within."

These movements -- all of which seem to make walking difficult -- "obviously tell people 'I'm a good victim,'" Grayson concludes. "Police note that many people who are assaulted are victims numerous times. This seems to support the notion that they're giving off signals.

"I think people do it unconsciously. I feel sure if they were aware of it, they could be taught to not walk that way. It would seem logical that if people could avoid these movements they might avoid being assault victims."