The only evidence that I find compelling when it comes to intelligent extraterrestrial life is the so-called 'Wow!' signal. Essentially, an Earth-based radio telescope detected an enormous
, unexplained radio signal from space in 1977. It's never been well-explained or even relocated (which was made trickier by the configuration of the receiver) but wasn't an atmospheric phenomenon and I'm of the view that it's the best evidence we have of extra-terrestrial intelligent life.
That isn't, though, enough to make any kind of statement of verification or anything other than an unexplained incident - albeit one that is consistent with some of the current theories of interstellar communication. Combine a few dozen of those incidents with a regularly-occurring pattern and there might be more to it.