Discovering life, or fossilised life, within our own Solar System would be a start. But if that life were earth-like (carbon etc) then it would prove nothing - ie bacteria-like life on Mars could simply have originated on the early Earth and been transported there after a giant meteor strike...or vice versa (we're all Martians in origin...??).
BUT if life can cross 25m miles of void, then there's the possibility life could have originated virtually at the dawn of time and transported itself in many different directions from one place. That means there could well be Earth-like beings elsewhere, maybe manyfold. However, as we (humans) have only been on Earth an miniscule amount of time, and we kill ourselves off, then if that is repeated throughout the universe then the percentage chance of saying "hello" is back to miniscule. We need at least two civilisations to hang around. For a very long time.