Powerful Radio Signal from Deep Space
One thing that I wonder is whether we could ever identify an alien communication signal as an alien signal is likely to be much more advanced.  In that scenario, the alien civilization is likely to be able to send their signal at the Shannon limit.  Additionally an advanced civilization is likely to be sending signals optically instead of over radio waves.  But even if we assume radio waves, Shannon says that the you can send the most information when using a random code.  As you approach the Shannon limit the signal becomes more noise-like as the encoding tends towards random.  So it’s entirely possible an alien signal is likely to look like pure noise to us and hence we may miss a true alien signal.