New York City is on high terrorist alert due to the Boston Marathon explosions. Here's a picture of Time Square as it is currently lining up with police cars. According to AP, The New York Police Department is increasing security at hotels and at the World Trade Center.
"More than 1,000 counter-terrorism officers were mobilized, along with the thousands of other officers on patrol. Highly trafficked areas like Times Square, Rockefeller Center and St. Patrick's Cathedral in Midtown Manhattan, the United Nations, and the World Trade Center site were being especially monitored, police said."
Mayor Bloomberg says that the police force deployed is there to protect the city if anything were to happen. "Some of the security steps we are taking may be noticeable. And others will not be," he explained.