Signage—the kind we see on city streets, in airports, on highways, in hospital corridors—is the most useful thing we pay no attention to. When it works well, it tells us where we are and it helps us to get where we want to go. When it fails, we miss trains, we’re late to appointments, we spend hours pacing the indistinguishable floors of underground parking garages, muttering to ourselves in mounting frustration and fury. And in some cases, especially where automobiles are involved, the consequences of bad signage can be fatal. Slate presents an excellent article about the Secret Language of Signs.