Sign Language

I could be wrong, but I always thought that signs were designed to help people who don't understand the words...To illustrate, if you will, a single cohesive idea that can be expressed visually rather than verbally. That is, before I moved to this planet. This is the sign you often see on the back of an elevator door. For days I wondered why a crab was on an elevator. A crab? An elevator? Beware of crabs? Of course after days of wondering and consulting some Japanese friends, I realized it's a warning not to get your hands pinched in the doors. This seems perfectly normal to Japanese people....I find it deeply odd and hugely confusing, hmm, like just about everything else here.