In the scant few decades in which humans have pursued radio astronomy, there has never been a real signal from the depths of space, something manufactured, something artificial, something contrived by an alien mind. There have been false alarms. The regular time variation of the radio emission from quasars and, especially, pulsars had at first been thought, tentatively, tremulously, to be a kind of announcement signal from someone else, or perhaps a radio navigation beacon for exotic ships that plied the spaces between the stars.
