The neon sticky notes covering the walls of Rosa’s Fresh Pizza in Philadelphia were not the idea of an interior decorator, but they’ve become the restaurant’s trademark. Each one represents a credit for a slice of pizza that a customer has purchased for a homeless person.

Rosa’s owner, Mason Wartman, says that through this unofficial program for feeding the city’s poor, he has handed out 8,400 slices of pizza to the local homeless population over the past nine months.

“The homeless, they come in and say, ‘I hear you give out free pizza to homeless people,’ ” Wartman told NPR blog The Salt.

The 27-year-old Philadelphia native opened the pizzeria after three years working on Wall Street. A few months into his venture, a customer paid a dollar extra, asking to buy a slice for the next homeless person who entered. Wartman stuck up a note as a reminder. Word spread, and soon there were sticky notes covering the walls.

The practice has become part of his business model. About 30 to 40 people come in each day for a free slice. According to Wartman, the purchases account for about 10 percent of his sales.

He told the Pittsburgh Post-Gazette that people’s generosity doesn’t just fill empty stomachs.

“I knew it saved people money,” he said. “I hadn’t considered that it stopped people from committing crime.”

Wartman’s pay-it-forward program stands in contrast to many U.S. cities’ treatment of their poor and homeless population. Many continue to pass laws that criminalize living on the streets. In Arizona, a lawmaker is cosponsoring a bill that would prohibit the use of EBT cards, used by 46 million Americans, at fast-food chains.

Now only if policy makers could demonstrate the same generosity of spirit as Wartman’s customers.

“They’re just really nice people, you know?” he told The Salt. “Sometimes homeless people buy them for other homeless people.”