I think this is one of my all time favorite signs:
There is one situated in each end of a tunnel in a small rural place in Norway. I'm not talking about the big 3,8m sign. This is all about the little brown box, actually a painted mailbox. Inside there is a torch light that cyclists with insufficient light on their bikes can borrow to get them safely through the unlit tunnel. At the other end there is a similar box, to leave the torch light in, for the next cyclist.
How cool is that?
Look for more cool signs here.