The “thumbs up” sign was originally thought to have come from the Roman Coliseum, where the fates of gladiators were decided. Other studies suggest they come from WWII pilots signalling each other in the air. But wherever it derives, the positive “thumbs up” in Western cultures is a big no-no in other countries, such as Greece, Italy, and some throughout the Middle East. It’s essentially the equivalent of the middle finger, which is why you should keep your thumbs safely tucked away if you aren’t sure about the custom.