Right underneath the image, in stencil-like lettering, the poster tells him: “Grandmaster Flash played the records they clapped for/ back when the dancefloor was packed at the Black Door.”

“I was like, wow, I didn’t know he was from around here,” said Mr. Arzu, who, at 19, is too young to remember the days in the ’70s when that artist first started entertaining crowds at a small club on Boston Road, just a block away, called the Black Door.

The poster did not exactly announce where the Black Door had been, but Mr. Arzu gathered it must have been nearby. Mr. Arzu, who lives in the Forest Houses, a public housing project in the Bronx, had seen similar posters of the hip-hop artist Fat Joe in his own neighborhood, where he knew that artist had grown up. He figured the posters in his grandmother’s neighborhood were doing the same thing, commemorating a local legend.

Mr. Arzu had no idea who had put the posters up, but he was glad they did. “It goes to show that when hip-hop started, that a lot of greats came from here in the Bronx,” he said. “It makes me proud.”

The origin of the posters, which were posted last November in 10 historical hip-hop sites around the city, is not exactly what you would call street. Claudia Burnett and Masha Ioveva, two multimedia artists at R/GA, a digital advertising agency near Times Square, were inspired by a request from the Bronx Council on the Arts (which ultimately had no hand in their project) to generate a digital experience for the borough that would celebrate its culture. They decided to create posters that would showcase the hip-hop history of the Bronx, and that would also invite passers-by to add their own rhymes by text message to Bronxrhymes.org, creating a virtual space for rhyming battles.

The two women, using funding they received from a digital arts organization, hired a designer to work up the posters, and asked a work colleague, an informal hip-hop obsessive named Steve Caputo, to work up the rhymes. The two women had approached a few hip-hop artists, and one did deliver a few. “But Steve’s were better,” said Ms. Burnett.

The humor in their devotion to the project wasn’t lost on Ms. Burnett. “There we were one Saturday morning, three white girls, two of whom are Bulgarian” — Ms. Ioveva, who is Bulgarian, brought a friend — “out there wheat-pasting posters, driving around in some Mazda rental car,” she recalled.

The making of history is one thing; the memorializing of it is another, and the people responsible for each contribution often have little to do with each other, except, ideally, a mutual appreciation.

But it can be a tricky, redundant business, bringing history to the people who lived it. A sign in Morrisania pointing out that Grandmaster Flash used to live there must feel, to a lot of its 40-something residents, a little bit like a sign on Pennsylvania Avenue pointing out that President Reagan used to work nearby. Did Hakim Milton, a 44-year-old man walking down Boston Road, know that Grandmaster Flash used to play at the Black Door down the street? “Yeah, and he lived right down there,” he said, pointing to an apartment building a block or two away. “And I used to see him play in the park.”

Near the Franklin Avenue Armory shelter, some Bronx Rhymes posters, now tattered, commemorate the time that the rap artist KRS-One spent living at the shelter. A man sitting in an S.U.V. down the street on Saturday afternoon — “Call me Mr. Smith,” he requested — was asked if he had known that KRS-One used to stay there. “Yes, I did,” he said.

How did he come to learn this bit of hip-hop trivia? “I used to see him walking in and out of it,” he said. “I live right down the street.” As much as he admired KRS-One’s work, he wouldn’t say if the posters had moved him one way or the other. “Doesn’t change my life one bit,” he said. “He got out, God bless him. I’m still here.”

The Web site hasn’t exactly taken off the way that Ms. Burnett and Ms. Ioveva imagined it might. So far, they’re not sure that even one passer-by has been inspired by one of their posters to text-message a rhyme. But because of some percolating buzz in the blogosphere about their project, people interested in the subject have sent in a few rhymes. Ms. Burnett and Ms. Ioveva expect the interest will only continue to grow, long after the last of the posters has been torn down or beaten down by weather.

The project may have its physical grounding in the Bronx, where the history is familiar to a lot of the locals, but the hope is that the information it disseminates will go mainstream, much like hip-hop itself, informing, however subtly, the way that people think about the Bronx, about art, and the recent past. “Keeping it real, homeless was his deal,” reads one rhyme posted on the site, about KRS-One. Another reads, “This site is wack, gotta get back, to what is real, ya know the deal?”