To many people, ghost bikes are the thing you drive by without noticing, or the curiosity that catches your eye as you walk past, then forget. Cyclists can't help but see them, and remember.

The white-painted bicycles, erected at or near deadly crash sites, are one way that cycling communities worldwide channel their grief when a biker dies. It pays tribute to those lost. It reminds drivers and cyclists to pause, and to be aware. And there's too many of them around Boston. Paul and Rebecca Larrabee-Albrecht are responsible for painting and preparing four of those bikes in the last six years alone, here in the Boston area.

Paul is about process, able to methodically detail the careful steps he takes to prepare each bike to properly memorialize the victims. Rebecca takes a different view, almost a mystical one — that ghost bikes are a way the fallen cyclist can "keep riding in the afterlife." She knows that's not exactly true, but part of her wants to believe it, or at least to seek some consolation in it.

"It's a tribute to the person that died, and also for the friends and family members to have something tangible to help them in the grieving process," Rebecca said. The couple's work started in 2009, when Tracy Milillo, 22, died in a bike crash on Longwood Avenue, just blocks from their Brookline home.

It went right to Rebecca's heart. The young victim was around her children's age at the time, and she felt compelled to do something.

She and Paul, cyclists themselves, had an unused bike at home. Paul stripped it down and added several coats of white paint; Rebecca put white silk flowers in the basket; and then they mounted it, quietly, near Coolidge Corner. In the years since, Rebecca has diligently adorned her own bike with flowers in a subtle, ongoing tribute of her own.

In 2009, the installation of ghost bikes seemed like an under-the-radar practice to the Larrabee-Albrechts. Paul said he saw them popping up around town, but didn't initially know what they were for. They were put up by friends, family, even strangers, like Paul and Rebecca. "Most people don't know what ghost bikes are until they walk up and see the plaques (with the cyclist's name on them)," he said.