That's not a problem, though, because a few kind people will stop and put them back as the community prepares for the second largest parade of its kind in Pennsylvania.
"It's what makes Canonsburg unique," borough police Chief R.T. Bell said Monday, nearly a week after the chairs began to appear on Pike Street.
People tie white plastic chairs together with twine or even crime tape. Others put out benches and beach chairs and top them with bricks or two-by-fours to keep them in place for the parade, which has attracted as many 60,000 people in the past.
"This is mild so far this year," Bell said as he viewed the parade route. "Usually, you can't find the sidewalk."
Although in previous years borough officials talked about prohibiting the tradition, Canonsburg manager Terry Hazlett said there's no law stating when chairs can be set out and "considerable pressure" to keep it that way.
He has seen news of the chairs on CNN's news crawl, and Jay Leno and David Letterman also mentioned it on their late-night talk shows.
Bell's concern is the wind, which already has sent a few of the aluminum chairs off the curb and into the street. But he said motorists are aware of the situation when driving through town these days and often stop and place them back on the sidewalk.
But neither Bell nor Hazlett fear the chairs will disappear. For some reason, no one ever steals the furniture, either. Bell has noticed that some who put "ratty-looking" chairs on the parade route will replace them Saturday with nicer seats.
"Believe me, people have gotten this down to a science," he said.
Down the street at Canonsburg General Hospital's Ambulance Service, manager Des Donohoe said the appearance of the porch furniture just points to the community's pride in its annual parade.
"The community really steps up," Donohoe said. "Everybody wants to be at the parade. It's a big deal."
But he's not yet welcoming any chairs outside the building.
For now the property at the ambulance service is bordered with orange traffic cones to block chairs. The cones will come down Saturday, Donohoe said, but for now he has to make sure that his ambulances can get in and out of the garage.
"We just want to keep it open for right now," Donohoe said. "It's safer that way."