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Police departments nationwide are urging their officers to be extra vigilant in response to Saturday's fatal shooting of two New York city police officers who were sitting in their patrol car.

In cities large and small, some police departments have ordered their officers to patrol in pairs, providing an extra set of eyes to watch for threats.

"The families of the officers throughout the city are upset," said Maurita Bryant, Pittsburgh's Assistant Police Chief. "They are nervous, they are fearful for the safety of their loved ones."

Washington, D.C. police got a similar message, and were told to remain vigilant and constantly aware of their surroundings, "while on duty on patrol, while stationary in a vehicle, and while in off-duty status."

In Northern Virginia on Monday, police academy graduates who are about to be assigned to the communities of Arlington and Alexandria said the New York shootings are on their minds.

"It makes me worry a little bit," said Andrea Bauman. "But I know we are all here to do a job."

Richard Vergera, who received his police diploma Monday after serving two tours in Iraq as a U.S. Marine, said the New York shootings were sad for everyone in law enforcement.

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"You are always scared. It's natural to be scared. It's what you do when you are scared."

Over the past decade, the number of police officers shot and killed on duty has averaged 54 a year. Including the most recent deaths, this year's number is below that, standing at 49.

But Craig Floyd, Chairman of the National Law Enforcement Officers Memorial in Washington, said the number of ambush killings so far this year is twelve, three times the yearly average.

"There's a lot of anti-government, anti-cop sentiment right now. Who is the most visible and vulnerable symbol of government in this country? It's the law enforcement officer, in uniform, walking the streets of America."

He called for demonstrators to tone down their rhetoric when protesting the recent killings of black men by white officers.

"Let’s realize that we all have a common interest in safe communities, and providing it is a partnership. Let’s rally around law enforcement and against lawlessness."

At the Justice Department, officials said there’s a place for constructive criticism of police abuses while still supporting the vast majority of officers who do their jobs well.

"I think what you have to be able to do is have a conversation about isolated instances of where we see profiling or where we see excessive force. At the same time, we have to make sure that our officers are safe and that we do everything we can to make sure that the brave men and women who are part of law enforcement are protected as much as we can," said Deputy Attorney General James Cole.

Many departments, from big ones, including Los Angeles, to smaller ones, such as the sheriff's office in King County, Washington, are directing their officers to wear black on their badges, in honor of the officers killed in New York.

And back in Pittsburgh, Maurita Bryant, the assistant police chief, is asking residents to put a blue light in their windows, to send a message.

"Although it may seem like the community is against the police, there are so many people that love our officers."

IN-DEPTH