Spring has finally arrived in Boston — and Boylston Street is buzzing. Outside Marathon Sports, a bricklayer fixes the sidewalk, as tourists mosey by and Red Sox fans hustle toward Fenway. A few feet away, workers install scaffolding at the marathon finish line.

There’s no reminder of the devastating blast that occurred here two years ago — except one. On a lamppost, someone has tied a garland of handmade, blue-and-yellow cloth flowers. There’s an identical memorial down the street, at 755 Boylston, where the other bomb exploded. But as the crowd passes by, barely anyone seems to notice it.

The sites of the bombings could be unmarked for a while — or even, forever. Because right now, there’s no clear process for deciding when a memorial will be built, what it will look like — or whether one’s going to be built at all.

"It’s really not up to me," said Boston Mayor Marty Walsh. "It’s up to the families and the victims and the survivors."

Walsh knows that commemorating the attacks is important. On Wednesday, the mayor is launching One Boston Day, an annual event that combines community service with remembrance.

"I think [commemorating the people who died or were injured] will always be a part of One Boston Day," he said. "And that’s the reasoning behind One Boston Day, is taking tragic losses for families, and turning the memories into positives."

As time passes, Walsh says, we may discover that a permanent memorial isn’t necessary.

"It’s really about what the families want to do," he said. "If we want to have a memorial we will work to have a memorial, and if they feel One Boston Day or another way of honoring the memories of their loved ones who were hurt that day — we’ll do that."

If there’s any consensus around the memorial issue, it’s that the victims should take the lead.

"In many ways, I would defer to the survivors of the incident, and the families who were most sorely impacted," said Meg Mainzer-Cohen, the head of the Back Bay Association, which represents local businesses. "I would find out where they think it should be."

That said, Mainzer-Cohen says she likes the idea of a physical space that fosters reflection — and that for her, there’s one ideal location.

"I would like to see some kind of memorial built in Copley Square," she said. "I don’t know whether it’s a statue, a fountain, some kind of mobile that would be a moving structure."

In the meantime, there’s another option for anyone who wants to ponder the attacks and what followed.

"We have all of the paper items here," she said. "So that’s over 10,000 pages of paper. We also have a sampling of the artifacts, shoes, stuffed animals — we can turn here.

Two years ago, archivist Marta Crilly helped dismantle the impromptu memorial that sprang up in Copley Square after the bombings. Now, she watches over the remnants at the city archives in West Roxbury.

"So this for instance is a section of chain," she said. "It’s a very small section of chain, it’s blue and yellow, thousands of messages."

Most items taken from Copley Square are stored offsite to conserve space. Still, the collection here is rich: There are marathon bibs, poster boards packed with goodwill messages, a flag sent from Bagram Airfield in Afghanistan. Arrayed on metal shelves in a room the public doesn’t usually see, they pack a special power. And the public is welcome. All it takes is some advance planning.

"They can call ahead or email," Crilly said. "Email is sometimes easiest, our email address is archives@boston.gov. We’re open 9:30 to 4:30 by appointment, and we set up a time that works for them so they can come see it."

It’s not what springs to mind when you imagine a memorial to the Boston Marathon bombing memorial. But it’s surprisingly affecting. And for now — it’s all we’ve got.