A few weeks ago, I noticed that my neighborhood had sprouted a suggestion box. The cards and pens disappear quickly, but are restocked frequently. One clever bit is that there are two slots: a private one, guarded by a combination lock, and a public one that can be opened by anyone. Anyone can read all the public submissions, and that's most of the fun. It's a fascinating collection. My favorite so far is something like "Someone should figure out what the ants are up to over by that tree", to which someone else added a few choice words of agreement. (I haven't found the ants yet, but I'll keep looking.)
There's an sfzero.org tag on it, so it wasn't hard to track down the people who put it up. Their description uses typical modern art language, so it's a bit pretentious for my tastes, but I like the box and I've enjoyed chatting with people around it.