ROTTERDAM, the Netherlands -When a McDonald's here was burglarized a few years ago, its managers decided they needed a new security system.
The police in this rough port city were offering an employee-activated device that sprays a fine, barely visible mist laced with synthetic DNA to cover anyone in its path, 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 McDonald's prominently warns: "You Steal, You're Marked."
The police 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 warning of its use -for what they call a precipitous decline in crime rates (though they did not provide actual figures).
"The whole thing is prevention, not about recovering stolen goods or capturing criminals," said Donald van der Laan, whose company, the Rhine Group, distributes the spray. The DNA is identical to human DNA, he said, "though there is a different sequence of components." Much of the spray's effectiveness, he said, comes from DNA's mystique. "No one really knows what it is," he said. "No one really knows how it works."
At the McDonald's, the DNA liquid is contained in a box the size of a large paperback book, mounted over an entrance door. "You don't smell it; you don't see it; nobody knows it's there," said Jean-Paul Fafie, the manager.
Dilek Gokceli, 30, a customer, said she had not noticed the sign. But she said she felt reassured: "It's for my sake, if there's danger."
The city is pushing the use of the spray and sometimes assuming the cost. It is also promoting the use of a kind of DNA crayon with which items like computers or cameras can be marked.
Creative Factory, which houses innovative start-up companies, began using the crayons after electronic equipment was stolen.
"We are surrounded by crime-ridden areas," said Leo van Loon, the executive director.
Along Beijerlandselaan, a shopping street, Jale Sag has owned Gulnar jewelers for the last three years and has seen a wave of robberies peak and then recede. Partly, she says, that is the result of closed-circuit cameras that were installed all along the street, but also because the police department and the city paid for a DNA spray system to be installed in her store.
Down the street, Bart Vos, 51, a manager at a barge company, gazed in the window of Jansen, another jeweler outfitted with the DNA spray. "They see that sign," he said of potential criminals, "they think twice."