From Elizabeth Howell, at Space.com:
Would it be easy to determine if the source of a mysterious radio signal was aliens? Probably not. A new paper argues that contact with extraterrestrials will likely be discovered through a prolonged, incremental process rather than an instantaneous eureka-like moment. Eureka — what the ancient Greek mathematician Archimedes allegedly said when he cracked a tough science problem about water displacement — tends to be the exception in science rather than the rule.
…
Cirkovic said in an email that the community involved in the search for extraterrestrial intelligence (SETI) should instead be prepared for a process that would take a very long time. It may take decades as the SETI community looks at all the reasons aliens might not be the source of a mysterious signal. More.
For one thing, a signal may not have been intended for us. If ever decoded, it could just be one side of a nasty let-it-all-hang-out dispute between neighbours.
See also: Astronomer: Why the search for aliens is a good thing
But surely we can’t conjure an entire advanced civilization?
and
How do we grapple with the idea that ET might not be out there?