Lately it has become a hobby of mine to fold little paper cranes from sticky notes and leave them in public, in visible places that people don't tend to go. Sometimes it's surprising how long one will stay there, given how many people must walk past it regularly.
In a way, it's a bit like graffiti, I suppose. I "tag" my locations with my creations, and it is definitely a signature. It's just not permanent. I understand why people mark places like that, though. It's a weird little feeling of power to walk through a place and know that you've marked it as your own, even if nobody knows it but you.
Mokalus of Borg
PS - Maybe it's a kind of nesting instinct.
PPS - Which is a weird way to think about graffiti.