I was reading in the Market Day thread something about signs, but asides from the noticeboards in some apartment blocks I don't think I've seen signs around where players can post announcements. I would LOVE to see one, at least one in every center (where the subway stations are) - so people can advertise things they're selling or services, posts like the one about moving in and finding the previous owner's stuff, group projects and events, that sort of thing. It could be area-specific or worldwide, and would give us Penpersonship people with stacks of paper things to do with our time.
Not sure if this should be on Ideas or General, since it may be a feature I hadn't noticed, but if there isn't bring it on :)