A stepped-up police presence is evident across the city, from landmarks like St. Patrick's Cathedral to mass transit hubs like Penn Station and Grand Central. Heavily armed officers and K-9 units are on the lookout for signs of possible terrorist retaliation.
"You come out of a house of worship and then you see heavily armed men," tourist Yvonne Paredes said. "It's a little scary, especially in New York City."
"I'm a little scared, so I'm going to be very careful where I go over the next couple of weeks," straphanger Aaron Mintz said.
Some find the stepped up security comforting.
"You feel protected and safe," tourist Lisset Salazar said.
"I feel a lot better knowing that there's a lot of cops here and a lot of other people too," another traveler added.
News Copter 7 also spotted increased scrutiny of vehicles entering bridges and tunnels. At the airports, security lines are longer than usual.
The NYPD says it has no credible evidence of any security threats, but what if the threat is a so called "lone wolf?
An increasing concern for law enforcement is someone off the radar, someone acting alone.
Most security experts agree the face of terror has changed.
They point to the attempted bombing in Times Square one year ago this week as a prime example of the so-called "lone wolf" terrorist.
"These are folks that are inspired, but not instructed. They haven't gone necessarily to a training camp, but they have received information," former NYS Homeland Security Chief Michael Balbone said.
Faisal Shahzhad's home-made explosive device ultimately failed, but it and similar plots pushed the NYPD and other law enforcement to expand anti-terrorism efforts, from more surveillance cameras and radiation detectors to monitoring stockpiles and sales of fertilizer.
The owner of the Chelsea Garden Center on Manhattan's West Side says he doesn't mind the regular visits from detectives.
'It's good to have a network," David Protell said.
In fact, experts say the public's help will be essentially in tracking this new breed of terrorist.
In the Times Square case, a street vendor sounded the first alarm.
"If individuals see something and they do bring it to the attention of law enforcement, then they are a force multiplier," Balbone said.