I remember seeing plastic flowers and other stuff on one of the Overton Hill barrows a few years back, it was a memorial to a young man who had been killed.
http://www.themodernantiquarian.com/post/54071/overton_hill.html

But it is I think quite common for people to recognise a special landmark to commemorate people who have died. And dogs of course, Kelston Round Hill above Bath, which some of us would look on as a 'sacred hill' has the ashes of departed hounds and little wooden signs, plus of course a planted tree dedicated to someone's mother (with withered plants underneath which was a pity). And just along the Cotswold Way under the hill is a stone remembering a young girl who died of an ashma attack whilst out riding and must have died alone up there, its very poignant...
All the stuff is transitory anyway.