New York City increased its police presence in the subway system.
The NYPD says it's just a precaution. The department stressed Monday that there's no immediate information indicating a specific threat to New York City.
Shortly after 6:00 p.m. Monday, they arrived at St. Patrick's Cathedral in Midtown, an NYPD Hercules team of heavily armed police officers and K-9's.
The public display of force and intimidation brought anxiety for some and relief for others.
Transit centers also saw stepped up security.
Police performed random checks as they searched passengers' bags inside Penn Station.
Patrol officers monitored subway platforms and rush-hour commuters across the city.
Newscopter 7 spotted additional scrutiny of cars and trucks passing through city tunnels and across city bridges.
Police officers were stationed outside the north tube of the Lincoln Tunnel, while other Port Authority cops surveyed the toll plaza at the George Washington Bridge.
At the airports, passengers endured longer than normal delays to pass through security screeners, and on this day, the long lines brought no frustrations at all.
"I am relieved, I'm fine with that. We have no problem flying today," said Linday Babion, an airline passenger.
"Our premise is bin Laden's disciples would like nothing better than to avenge his death in New York again," New York City Police Commissioner Ray Kelly said.
Earlier Monday, one unruly man was arrested at Penn Station and was met by a swarm of Amtrak officers looking to quickly quell a disturbance.
"We all need to continue to be cautious and probably will be for the rest of our lives," said one commuter.
"This is not a time to take anything for granted," Governor Andrew Cuomo said.
Riders were reminded that if they see something they should say something.
The NYPD said all members of the service remain alert in the aftermath of the announcement that Osama Bin Laden has been killed.
Meantime, they seemed to be everywhere: armed National Guard units patrolling New York's airports, along with more Port Authority Police.
It is real visible signs of heightened security as officials and travelers weigh the possibility of al Qaeda striking back.
"Waiting for something to happen, who knows? You never know, I'm sure they're upset," said Dean Willis, a traveler from Chicago.
Some said they had no concerns about traveling in the wake of bin Laden's death.
"No I don't. I thought about it a little last night, but with security we have in this city I feel fine," said Pat Barron, a traveler from St. Louis, Missouri.
While there is no specific threat, the Port Authority says it has added more police at its airports and vows to continue to make its facilities safe and operational in the days ahead.
These added measures are prudent when considering al Qaeda's obsession with airports and airplanes.
An aviation security expert says the pressure has never been greater for bin Laden's followers, homegrown or abroad, to attack.
But Abdul Dardery, a Muslim heading home to Minnesota, approached Eyewitness News before boarding his plane at LaGuardia Airport to say he doesn't expect retaliation because al Qaeda, he says, is dying.
"I think al Qaeda is part of the past and let us put it as part of past. Let this fear we really need to take it out of our hearts and minds it only breeds prejudice," Dardery said.
In Los Angeles, police were stepping up intelligence monitoring, and New Yorkers will see extra police at their airports, bridges and the World Trade Center site itself.
84 Port Authority employees died in the attack on the World Trade Center on Sept. 11, 2001.
Kelly issued a message to all police commands reminding them that while there's no information indicating a specific threat to the nation's biggest city, officers should remain alert.
The head of the House Homeland Security Committee said the U.S. must temper victory with vigilance in the wake of bin Laden's assassination.
Rep. Peter King said the al-Qaida terrorist organization could "try to avenge this death" and said "we'll have to be on full alert."
King also said there will be "round-the-clock" government surveillance to determine if al-Qaida is planning or organizing a retaliatory attack. He said federal agencies will be trying to find out if an attack is possible or imminent, "and how we can prevent it."
In Los Angeles, a top counterterrorism commander said police will be stepping up intelligence monitoring.
Assistant Commanding Officer Blake Chow, who heads the department's counterterrorism and special operations bureau, said Sunday night that officers will be keeping a close ear on intelligence buzz to develop immediate response plans accordingly.
Police in Philadelphia were on heightened alert, checking on mosques and synagogues every hour, Lt. Raymond J. Evers said.
Washington's Metro transit system also stepped up security.
(The Associated Press contributed to this report)