National Guard troopers keep vigil outside the police station in Ferguson, Missouri, on November 26th. Photograph by JEWEL SAMAD/AFP/Getty

On Monday afternoon, President Obama announced, as part of his response to the clashes between protesters and police that have occurred in Ferguson, Missouri, since the fatal shooting of Michael Brown by Officer Darren Wilson nearly four months ago, that he would be imposing stricter standards on the distribution and use of U.S. military equipment by local police forces. Current regulations, Obama said, were inconsistent and, often, inconsistently enforced.

The announcement came after the White House released a report reviewing the use of military equipment provided through federal programs, commissioned just after the Ferguson shooting in August. Over the past few decades, the report said, such programs had expanded significantly—in the five-year period between 2009 and 2014 alone, the federal government provided some eighteen billion dollars for them—but training on the safe and proper use of military-style equipment had not been instituted apace. And so, basic personal-protective gear, high-powered weaponry, and vehicles—categories encompassing everything from night-vision devices, body armor, and full SWAT gear to Tasers, small arms, sniper rifles, and Humvees—were often requisitioned without the necessary guidance on how to properly deploy them. “When police lack adequate training, make poor operational choices, or improperly use equipment,” the report stated, “these programs can facilitate excessive uses of force and serve as a highly visible barrier between police and the communities they secure.” Or, as Senator Claire McCaskill put it back in September, “Officers dressed in military fatigues will not be viewed as partners in any community.”

To address the problem, the report—and President Obama—suggested a multi-pronged approach: more standardized federal oversight of how the equipment is deployed; and expanded training, to say precisely when and how military equipment should be used (the latter would also include the addition of fifty thousand body cameras). But will more considered use of military-style gear help to prevent violence in Ferguson-like situations in the future?

Tempering the conditions under which police can use military-style gear makes a certain amount of sense: uniforms really do set people apart, and the specific nature of a uniform can send strong social signals. They allow us to tell, at a glance, who someone is and what she is apt to be like. A white coat and stethoscope, or a set of blue scrubs, for example, tells you that you can ask for medical help and expect to receive care. And a navy blue shirt tucked into navy pants, with cap and badge to match, indicates that someone responsible for enforcing the law—in a very particular way—is in the area.

Since London’s Metropolitan Police service issued the first police uniform, in 1829—a dark-blue number, similar to the one in use today in the United States—the outfit has sent a very specific signal. One of the original reasons for its color and style was to distinguish it from the red-and-white uniform worn by British soldiers. It was supposed to be clear that one was for day-to-day local policing, the other for serious armed conflicts. You could ask the man in blue for directions, or for help finding a misplaced wallet. The man in red and white was attending to more vital business—business that, almost by definition, involved violence. People in many countries have now had almost two hundred years to learn and internalize this distinction.

So what happens when the barriers begin to shift, and the traditional blue is, on occasions when local forces think it’s warranted, like at demonstrations or other public gatherings, being replaced by something quite different? There are currently no federal regulations monitoring when police can swap blues out for SWAT ensembles; that determination is entirely local—and, as Peter Kraska, a professor of criminal justice at Eastern Kentucky University, has documented, it is also increasingly common, having occurred approximately fifty thousand times this year, up from three thousand times in 1980. Few of those deployments, he says, are in response to violent or life-threatening crimes; in fact over eighty per cent are “proactive” (that is, not in response to a specific threat).

The decision of which gear to use in a given situation can have deep repercussions. Richard Johnson, a professor of criminal justice at the University of Toledo who has been studying the role of uniforms in perceptions of police for a decade, has written that an “officer’s uniform has a profound psychological impact on others, and even slight alterations to the style may change how citizens perceive them.” The traditional uniform, he has found, often evokes impressions of safety and competence. Fatigues, SWAT suits, and other military-issue gear associated with the army, by contrast, suggest increased aggression. The implication, for those being policed, is that they require extreme measures.

In 2007, Ernest Nickels, a professor of criminal justice at SUNY, Oswego, showed a group of a hundred and fifty students photographs of two different policemen, one white, one black. One was shown in a relaxed pose, with arms at sides and a pleasant facial expression; the other looked assertive, with one foot forward, one hand raised to signal “halt,” and the other on the butt of a firearm. Nickels then digitally altered one aspect of each photograph: the color of the officer’s clothing. The students were asked to rate each picture on a series of seven-point scales covering ranges of good to bad, nice to mean, gentle to forceful, passive to aggressive, and friendly to unfriendly, among others. Finally, the subjects were questioned about their prior encounters with police, both in person and in the media.

As expected, the students viewed the officers posed in the aggressive stance more negatively than those in the relaxed stance. But something else emerged, as well: uniform color played an important role in perceptions of aggression, regardless of the officers’ stance or the students’ prior experiences with police. Officers in dark uniforms were rated as friendlier, more honest, and better over all than those who wore light-colored uniforms. The implication was that, over time, darker outfits, including the traditional police navy, have become associated with local, diurnal order—and lighter, military-style deviations (green, khaki, white) with order of a very different sort. Indeed, in one of Johnson’s earlier studies—which Nickels had used as a model for his own—a test group of approximately seven hundred and fifty citizens of a Midwestern city gave a khaki-uniformed officer its lowest possible average rating, on the same set of seven-point scales that Nickels used, and a navy-blue uniform, its highest.

In fact, changing any aspect of police dress, even to more casual civilian-like attire, tends to backfire. In 1984, the Stanford psychologist Robert Mauro (now at the University of Oregon) looked at the results of a real-world experiment from Menlo Park, California, in which the police force had, for eight years, starting in 1969, worn more casual attire in an effort to improve community relations. The change, Mauro found, did not have the hoped for results. To understand why, he replicated the conditions of the Menlo Park program in a controlled laboratory setting. Again, traditional uniforms scored best—deviations, even friendly-seeming ones, increased negative perceptions of police.

There is, too, the other side of this relationship: how what people wear affects how they act. Military gear may harm relations between police forces and citizens not only because they signal violence but because they may, in some sense, cause more violence. The same cues that signal “army” and “conflict” to civilians may affect police officers themselves. When they “dress up” for serious engagements, for example when donning SWAT gear to respond to a riot, they no longer feel like local law enforcement anymore but like part of a broader military machine.