Near 10th and Market Streets, Edward Dunn held up a piece of cardboard on which he had scrawled a plea in the form of a question.
"What if God occasionally visits Earth disguised as a homeless guy panhandling to see how charitable we are?"
A minute later, an answer walked up: Texas-based artist Willie Baronet.
He offered to buy Dunn's sign, but not for the sake of charity or even religion.
Baronet, 54, is embarked on an unusual, long-term project, purchasing the signs of homeless people and turning them into exhibits, seeking to make people consider the meaning of home. It's called "We Are All Homeless."
"It's really meaning, 'We are all the same,' " Baronet said. "If there's a person on the street holding up a sign, at a basic level, it's someone asking for help. The title means there's no us or them. It's just us."
Dunn, 38, was eager to sell - as are most people whom Baronet approaches. His eyes were glassy, his arms scarred, his skin itchy. He asked $40 for his sign, but settled for half.
"I had a more generic sign before," he said. "I wanted to go in a different direction, be a little more innovative."
Baronet sought more than Dunn's sign.
"What does home mean to you?" he asked.
"Wherever I lay down at night," Dunn answered, "that would be home for me."
In Philadelphia on Monday, Baronet neared the end of a 31-day, 24-city trek in which he has bought scores of signs. In two hours on East Market and Chestnut Streets, the advertising professor at Southern Methodist University collected nearly a dozen signs and as many stories.
Baronet has pursued his obsession for more than 20 years. This month he made his first cross-country trip, buying signs from Seattle to Cincinnati and Portland to Pittsburgh, trailed by a crew filming a documentary.
After raising nearly $48,000 through Indiegogo to pay for the trip, he has bought about 230 signs. All together he has more than 800, each one different.
Some are miniature artworks, others crude and misspelled. They are comic or desperate, confident or pleading, written on pizza boxes, place mats, wooden planks, and ice-cooler lids.
Baronet doesn't pick and choose. He buys - or rather, offers to buy - the signs he sees.
"Outta beer," said a sign from Seattle.
"I am short $8 for an inhaler," said one from Albuquerque.
Others in his collection say, "My liver is a terrorist - help me kill it." And, "Vietnam done this to me!" And, "Have you ever felt invisible before?"
A longtime graphic designer, Baronet is drawn to the signs as artifacts: The style of lettering. The sweat stains. The choice of words. By nature, the signs are temporary and handmade.
Most people "are a little baffled at first at why I want them," Baronet said. "They think it's completely worthless."
Once he explains, many become interested. They want to tell their stories to someone who will listen.
On Market Street, near City Hall, Doug Nelson sat slumped against a light pole, tattooed from leg to arm to hand to neck. A barbell piercing glinted near his left eye.
"Unemployed Homeless and Hungry. Anything will help," his sign said.
Baronet introduced himself. Nelson, 34, quickly pulled notepads from his bag, the pages filled with elaborate drawings of anime figures.
Nelson said he was an artist too. He wants to start a tattoo business. Home, he said, is not a place but a people.
"It's my family," Nelson said. "It means my family."
He took $10 for his sign.
Generally, Baronet lets the homeless person set the price - "it's part of what changes the dynamic" - but he tries not to spend more than $25. Most people ask $2 or $5. He never pays less than $10.
A few days ago in Washington a man refused to sell. "Not for any price!" he told Baronet. A guy on the Las Vegas Strip said he couldn't take less than $150. Baronet wished him well and moved on.
The signs become part of art installations. Dozens may be merged into a giant, warehouse-wall-size collage. Or suspended from gallery-room ceilings. Or held up by people in a kind of homeless-sign flash mob.
As he traversed Center City, Baronet noticed a young man perched at the door of a Burger King, holding a tiny cardboard sign, smaller than a half-sheet of paper.
In almost-too-small-to-read letters it said, "I'm asking for food and drink not money."
The man happily sold it for $10.
"That was awesome!" he said, tucking the bill into his pocket. "That was, like, the coolest thing."
It is unclear exactly how many homeless people live in Philadelphia. Project HOME says 494 people were counted living on the streets in 2013. The year before, a study found that 12,053 people here had experienced homelessness.
The reasons are myriad: Drug abuse. Mental illness. Reductions in federal spending. Fewer jobs for the less educated. Changing housing markets that oust the poor.
Baronet has never been homeless. But for years, he said, he noticed he became uncomfortable when passing homeless people on the street. He avoided looking at them. That changed in 1993, when he started buying their signs.
More and more, his conversations with homeless people have become part of the art project.
"People tend to lump them all together," Baronet said. "Or make some judgment about why they're homeless. A lot of it for me is trying to get people to slow down, smile, see the human being that is in this predicament, and see each other's humanity."
Sympathy for the homeless can stand in a kind of hierarchy, he said, with people more willing to give money to the elderly and to women than to healthy-looking young men. And that thinking can be inaccurate.
"I've come across a lot of young men who at first glance you think are able-bodied," Baronet said. "But many of them are disabled veterans, or have mental-health issues. Many of them have PTSD. Many of them have burned every bridge in their life. If somebody doesn't have an address, it's difficult for them to get a job, any job."
Mandi Haney sat on the sidewalk outside a Market Street drugstore when Baronet approached. The 33-year-old said she has a job - the street is her workplace.
If she doesn't beg, she doesn't eat. She sold her sign for $10.
"Now I'm signless," she said, unconcerned. "I can make a new one."