They're 400,000 strong and the Pentagon sees them as an emerging threat

The Pentagon, the world's largest user of drones, has posted a new policy on signs outside the mammoth five-sided building: No Drone Zone. The signs, complete with a red slash through an image of a quadcopter drone, reflect America's growing concern about the proliferation of the small, inexpensive remote-controlled devices and the risk they pose to safety, security and privacy. Federal law prohibits flying a drone anywhere in and around Washington, an area known as the National Capital Region. Other communities and institutions across the country are wrestling with the potential threat from more than 400,000 private and commercial drones now registered to operate in the skies. The pilot of a commercial jetliner said his plane nearly collided with a drone while approaching Los Angeles International Airport on Friday afternoon, sparking a search by L.A. police and sheriff's officials for the owner of the unmanned aircraft.