On September 16, 29-year-old “Essam” and a group of friends blanketed lower Manhattan with posters designed to look like official New York Police Department signage. “Drones: Protection When You Least Expect It,” read the slogan below simple ideograms of families running from unmanned aerial vehicles. Essam and his team disguised themselves as employees of the outdoor advertising firm Van Wagner, which manages the advertising space on bus stations and kiosks throughout the city. All told, they swapped out about 100 ads, writes Katherine Mangu-Ward.