Another related issue that touches on this is the question of how to identify an artificial signal. The more advanced communication gets, the more compressed it is. You're unlikely to be able to spot obviously artificial things like repetition in a signal, because the compression will deliberately remove it.However, analogue signals, RF-transmissions, eventually also dies out over time because of solar storms, magnetic field influens, particle obstruction. So the result will over time become just noice that is already present in space, and not possible to interpret.
Nobody ever said finding another civilisation was going to be easy, after all.