Many years ago, when my daughter was at junior school, she came home with a stone with a smiley face on it. She had had a trainee teacher and his parting gesture, I seem to remember, was to give all the children in the class one of these.
Later, at the local church fete, my daughter set up a stall selling stones that (I had collected from a North Wales beach and) she had decorated with smiley faces. She called them 'Happy Stones'. She raised quite a bit for church funds and provided a lot of people with something that would remind them to be happy.
Some time later, in September 2001, I went away to a conference at the University of Cambridge. When I was unpacking, I found the happy stone above secreted in my bag. It is almost impossible not to smile when looking at and handling one of these things.