Pennsylvania State Police on duty over the holidays this year will be scanning the streets for problems -- and scanning windows for comfort in the form of a lone blue light.

Project Blue Light began in 1988 to honor police officers killed in the line of duty.

This year, the State Police saw that number tick up by one, when Trooper Blake Coble died in October after his patrol car was hit by a truck running a stop sign.

Trooper Adam Reed says citizens and businesses are once again being asked this year to include in their holiday display a single blue light that, for law enforcement, holds special significance.

"That way, if any officer driving past a house sees a blue light in the window, he'll know that his fellow officers are being remembered," Reed said.

The tradition started with a woman in Philadelphia who put up a blue light to honor her son, who died while serving as a city police officer.

Police departments nationwide have continued the tradition promoted by the group known as Concerns of Police Survivors, or COPS.