We have found lots of signals. The problem is failure to confirm = reasonable doubt. When we receive the same signal at 8 wide spread locations, the doubt then is: is this natural or sentient. Generally we assume a single unvaring frequency has to be sentient, but does it? How many parts per trillion variation is allowed? Does the amplitude also need to be steady? Could SETI detect even strong single sideband modulation, if the carrier is surpressed 100 db? In recent years, high power human comunication has used FM/FM and other complex modulation algorisms. ET may use systems we have not even thought about.
Let's suppose we record what appears to be data, video or audio. Can we translate it into English or something comprehencible to average humans? A few experts claim they have a good translation. Do we believe their translation is correct or even in the ball park? Some will believe; some will cry conspiracy. Most will sit on the fence rather than panic. I can't check the validity of the translation of Egyptian hyroglifics, can you? Most experts seem to be of the opinion that Sitins translations are worthless. The bottom line is: Few will believe sufficiently to change their life style significantly.
An other possibility is ET has been orbiting Earth about a million kilometers away for several decades, watching and listening to our transmissions. ET now knows a hundred of our languages and dialects and understands human nature and culture far better than most humans understand. Shortly ET will begin broadcasting to Earth with radio and TV programs which humans will find more interesting than the trash the mainstream media feeds us. Then common folks will learn, and modify their behavor in desirable ways. Perhaps even some of the intellegencia will be modified and improved. After a few decades of this brainwashing, we may happily allow millions of ET to land and intigrate into Earth's society. The long term results will likely be a mix of good bad and indifferent. If ET is intelegent enough to get here, they are likely wise enough to collonize Earth with a minimum of confrontation with us, the indigionous population. Neil