NEW YORK, UNITED STATES - SEPTEMBER 17:  A gun of New York City Police officer in a metro station is seen on the photo in New York, United States on 17 September, 2014. Security measures tightened on critical points of New York after Islamic State of Iraq and the Levant call for terrorist attack against New York on the social media. (Photo by Bilgin Sasmaz/Anadolu Agency/Getty Images)