Here’s author/photographer Geoff Dyer’s meditation on the ghost bike street memorial phenomenon:
As well as being part of a web of activist organizations, the ghost bikes can be seen in the context of the ad hoc accumulation of street art generally, from loutish graffiti litter to Banksy’s ironic—now ironically iconic and commodified—stencils, to community-based murals. In civic ambition the ghost bikes are like a quiet and respectful aspect of the old Reclaim the Streets initiatives—except they proceed from the premise that the streets do not need to be reclaimed by confrontation, that they are already ours. But the bikes also throw into relief something about the inadequacy of much public art generally and “official” memorial art in particular.