by liberal japonicus
A wander through some links turned up this Wikipedia entry.
A ghost bike or ghostcycle is a bicycle set up as a roadside memorial in a place where a cyclist has been killed or severely injured (usually by a motor vehicle) Apart from being a memorial, it is usually intended as a reminder to passing motorists to share the road. Ghost bikes are usually junk bicycles painted white, sometimes with a placard attached, and locked to a suitable object close to the scene of the accident.
This reminds me of something one often sees in the Deep South (and perhaps in other places), which is roadside memorials where people have had accidents. However, the impulse for those, I think, is less for traffic safety and more to commemorate the passing of someone, but I see a connection between the two. Any ghost bikes where you are?