This is what I mean by "knowing exactly what to look for."
Can we place something at Pluto and have it listen to radio waves from the direction of Earth, and compare it to the background "noise" at that location? How different is it? How much of that perceived difference would be our own bias?
How much evidence about life on Earth is available to our own instruments from this range? -> https://www.bing.com/images/search?q=Pale+Blue+Dot