The walls at Rosa's Fresh Pizza in Philadelphia feature Post-it notes from customers who contributed $1 so that local homeless people can get a free slice of pizza.
"The homeless, they come in and say, 'I hear you give out free pizza to homeless people,'" Rosa's owner, Mason Wartman, recently told NPR.
Wartman began the program last year after a customer asked if he could buy a slice of pizza for someone who was homeless.
"I said, 'Sure,'" Wartman said. "I took his dollar and ran out and got some Post-it notes and put one up to signify that a slice was purchased."
The customer told Wartman that he got the idea from Italy, where people buy coffee for those who cannot afford it.
According to Wartman, his customers have bought 8,400 slices of pizza for homeless people over the past nine months. Each day 30 to 40 homeless people get a free slice, and some leave notes thanking the paying customers.
Some Starbucks locations also have informal "pay it forward" systems, according to NBC News.
However, ABC News reported in 2014 that a Starbucks customer in Florida deliberately ended a "pay it forward" streak that had grown to 458 consecutive people because he decided that customers did so out of guilt not generosity.
In 2013, Panera announced that some if its stores would not have set menu prices, but would instead adopt a "pay-what-you-can" policy, noted the Wall Street Journal.
Sources: NBC News, ABC News, Wall Street Journal / Image Credit: ANBI