Redundancies are key to safety. Or so the story goes. As for anything else, there are tradeoffs. Informational redundancies are perilously close to noise – the very noise they are supposed to avoid. Noise is an information theoretic notion; information is a commodity out there, it is a publicly available structure in the environment. (Fred Dretske, Knowledge and the flow of information) But information is not the end of the story. Its relevance depends on the structure of the system processing it. Cognitive systems like ours are prone to fatigue. Repetition induces habituation. Redundancy may simply generate counterspecific effects. Twenty left arrows become decoration.

Not all of redundancy is repetition, or repetition within a single informational channel or format. Some objects afford specific behavior in virtue of their shapes. (J.J. Gibson, Knowledge and the flow of information) Good design is in part related to creating shapes with good affordances. Signaling is oftentimes trying to put a patch on poorly affording objects and situations. “Push” and “pull” signs on countless doors are a trademark of insufficient door design. Now, surely there was no point in designing a sliding door handle that resembles a turning door handle. But there aren’t many ways to open a sedan trunk, and once it is open, it is hard to figure out alternative ways to close it. Toyota probably thinks otherwise, at least on this 2007 Prius sticker. It is an interesting case of a redundancy across informational channels. The perfectly available affordance is dubbed by a cartoonish icon. As usual, our relevance-seeking brain starts asking questions: am I closing the trunk in the correct way, after all? Should I use my right hand or my left hand will just do? The actual intention behind the sticker is to indicate a concealed notch in the trunk door, that allows one to pull it down keeping at the same time one’s hands clean.