Marooned on a traffic island in the centre of one of London's more aggressive, unpleasant junctions, it is at first glance an almost discordant note of beauty: a bicycle completely painted a spectral white and covered with a mass of flowers.

But it is in fact a deeply gloomy spectacle. Commemorating Min Joo Lee, a 24-year-old fashion student killed last month while cycling through King's Cross, it is one of the latest examples in the fast-growing global phenomenon of "ghost bikes".

Often painted entirely in white and locked to a fixed object as close to the accident site as possible, ghost bikes aim to act as both a memorial –they feature the name of the dead rider and other details, whether on a sign or painted to the frame – and a cautionary reminder for cyclists and drivers about what can happen when bike and vehicle come into contact.

The practice can be traced back to the US in 2003, and now exists worldwide. A website tracking ghost bikes records several hundred, taking in locations as varied as Poland, Singapore and Mexico.

Despite their eerie poignancy, some cycling campaigners worry that the memorials could, in fact, act in the main to put off would-be cyclists. "While ghost bikes may help ensure road users pay more attention to one another, they make give the impression that cycling is more dangerous than it actually is," said Chris Peck, policy co-ordinator for the CTC, the UK's main national cycling organisation. "Cyclists in general live two years longer than non-cyclists and are in general healthier – even in heavy traffic, a three-mile ride to work is healthier than driving to work every day and failing to get any exercise."

The first recorded ghost bike was in St Louis, Missouri, in 2003. A man who witnessed a fatal collision decided to mark it with a painted bike bearing the message, "Cyclist struck here."

The first documented UK example commemorates James Foster, a London-based Australian man struck by a speeding drink-driver in Islington, north London in 2003. Colleagues at the cycle shop where he worked, Mosquito Bikes, erected the ghost bike on the fifth anniversary of his death. Yet now staff at the shop admit they are unsure about the general practice.

"Even though the shop has this personal connection with James, we've got mixed feelings about them," said Gill Ord, a director. "Personally, I'm not sure other riders pay much attention, and there's a danger they can put people off cycling."

Cycle safety, particularly in big cities, remains a vexed and much-debated subject. While the number of cyclists killed on the UK's roads rose slightly last year, campaigners say this must be seen in the context of a downward trend longer term, plus greater numbers of people on bikes. However, in London there has been alarm at the number of female cyclists killed in recent years in collisions with lorries, particularly construction trucks.

At the ghost bike marking Lee's death, most cyclists seemed to think the project was worthwhile. "There hasn't been much publicity about them, so though people see the ghost bikes, they don't necessarily understand their significance," said Tom Rosenfeld. "As a regular cyclist I know I can get very complacent – it is easy to forget about the dangers and assume that it will never happen to you. But when I see one they do make me reconsider my safety and reassess whether I am being careful enough."

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