These are 5 of the strongest signs that could suggest UFO Alien life exists. 5 Pieces of evidence that could prove UFO Aliens exist. Skeptics and believers are constantly battling each other as to whether or not we are alone in the universe. Though we have no solid proof of UFO Alien life, many state that we have enough evidence that could prove humans are not alone in the universe. So here are 5 possible signs that could prove aliens exist.