Hey, It’s Schrödinger’s Cat
We can rest assured that the cat in the picture isn’t actually missing. This is someone’s clever idea of a joke, based on Erwin Schrödinger’s 1935 thought experiment.
He imagined a cat being enclosed in a box with a radioactive source and a poison that will be released when the source (unpredictably) emits radiation. Until the box is opened and the cat is observed, the cat is considered to be simultaneously dead and alive according to quantum mechanics. This sign is a clever joke, but you can only understand it if you paid attention in class.