"It caught me off-guard, but what a sweet gesture," he said. "I hope we don't ... we never should forget."
Chief Jay Grimes of the Williamsport Volunteer Fire Co. said that in the days and weeks following Sept. 11, the public thought more about first responders. He said that back then, when he was on his way to an emergency, people would honk their horns and wave.
"Now, when you go by, they don't even know you're there," Grimes said. "I think people really understood for a while what we do, but now I think it's gone away."
Tim Smith, vice president of the Boonsboro Volunteer Fire Co., said time has blurred the memories of Sept. 11.
"Firefighters will never forget, though," Smith said.
Nearly 3,000 people died that day, at the World Trade Center, at the Pentagon and in Shanksville, Pa.
Horn keeps a Sept. 11 cloth patch on a bulletin board near his desk. The patch lists the number of firefighters and paramedics who died after the Sept. 11 terrorist attacks - 343.
While he looks at the patch each day, Horn said he frequently recalls images of the twin towers falling and of the battered Pentagon.
Horn was on duty that day and said a friend who was working at Washington County Emergency Services called the station and told him to turn on the television after the first plane crashed into the World Trade Center's North Tower.
He saw reports of a plane crashing into the tower and reporters saying "guidance problems" may have been to blame, Horn said.
"We saw the plane hit and I said, 'That's not guidance problems,'" he said.
When the second plane hit the South Tower, Horn said he knew what was coming.
Horn attended a class shortly before the attacks, and the instructor mentioned that an attack at the upper portions of the World Trade Center could level the towers, Horn said.
"So, when I saw that, I said, 'Those buildings are going to collapse,'" he said. "And it wasn't long."
When the towers fell, Hagerstown Fire Department Capt. Justin Mayhue said he immediately thought about the emergency personnel trapped inside. He knew they would be inside the buildings, helping scared and injured people.
"Of course, my worst fear was realized," Mayhue said. "I knew there were hundreds of firefighters inside."
Mayhue was working on the set of the Civil War movie "Gods and Generals" on Sept. 11. He heard only pieces of what was happening in New York and Washington, D.C., while filming that day.
When he checked the television that evening, he saw the rubble that had been the twin towers and realized the magnitude of what had happened.
"I think that's when it really set in," Mayhue said. "As a firefighter, I felt so removed and so helpless in that situation ... What can I do from where I'm at?"
He said the terrorist attacks caused the public to demonstrate its appreciation of firefighters and other first responders.
"I've been thanked for the job I do more in the last four years than I was in the first 20-plus years I was involved in the fire service combined," Mayhue said.