ROTTERDAM, the Netherlands  When the McDonald’s down from City Hall here was burglarized a few years ago, its managers decided they needed a new security system.

It was just about that time that local police officers were offering something totally different that they hoped would stem a rising tide of robberies that occur mainly in the immigrant neighborhoods of this rough-and-tumble port city. The new system involved an employee-activated device that sprays a fine, barely visible mist laced with synthetic DNA to cover anyone in its path, including criminals, and simultaneously alerts the police to a crime in progress.

The mist  visible only under ultraviolet light  carries DNA markers particular to the location, enabling the police to match the burglar with the place burgled. Now, a sign on the front door of the McDonald’s prominently warns potential thieves of the spray’s presence: “You Steal, You’re Marked.”

The police acknowledge that they have yet to make an arrest based on the DNA mist, which was developed in Britain by two brothers, one a policeman and the other a chemist. But they credit its presence  and signs posted prominently warning of its use  for what they call a precipitous decline in crime rates (though they could not provide actual figures to back that up).