Its a relatively new phenomenon that seems to have come from the continent. I remember travelling along a really scary road on Tenerife, looking over a sheer cliff to the rocks below, where people had put their lives at risk to place flowers and build monuments to their loved ones who had fallen over the edge.
Across here in Scotland there have been requests from the police and emergency teams to stop this practice which has been known to cause further accidents as drivers try to see what the flowers are for.
The other thing that bothers me is the kind of public ownership of well known people, which demands that memorials be placed for the benefit of their fans and admirers. This is sometimes also against the wishes of the owners of the place they want to put their memorial.
All part of the whole "celebration of grief" that we saw at its extreme when Diana died. That's very difficult for the people close to the person who died, who deserve our sympathy and respect at that difficult time, but also privacy and their choice of how their loved one is remembered.
Most people would rather be remembered (or have their loved one remembered) by some practical thing like help for others, such as The Joey Dunlop Foundation, the Hailwood Foundation etc.
Sorry about the rant, but I have seen the distress this involvement of well meaning outsiders can cause.