I saw an object that no one can Identify. Therefore it must be an ET spaceship!
It is easy to see that the above argument is fallacious. Yet people have often waged a battle on whether or not there are 'UFOs'. An ET sceptic, for instance, spends too much time debunked UFO photographs. You see, this Meier's photograph is just an optical illusion. It is, as if debunking the ET hypothesis reduces to showing that there is no real UFOs. But, of course, you know what would happen in case it becomes clear there are UFOs out there. They shift the battleground to the issue of whether or not the objects are realy the ET spaceships. Common sense should tell you that a sceptic should not have spent too much time debunked UFOs if such objects, if real, doesn't prove anything. In other words, if unknown objects up there doesn't prove anything pertaining to ETs, then it is not worth the hype.
At the other side of the coin, the ET proponents spends a lot of time showing people photographs and videos of strange objects up there as if this is all what it takes to prove that ETs are here! You see, there is an object there that seems to defy known laws of physics, there is an object with strange shape up there, even trained pilots or soldiers cannot identify it, and other yada yada. What do existence of such objects prove, apart from proving that we are ignorant of our sky?
We cannot rely on ignorance to give a positive proof! We cannot say 'scientists cannot explain such, therefore it is the acts of ghosts'. We must give a positive evidence, and not point to a lack of one, at the other, often sceptical camp. In the case of UFOs, (and other cases), it is ridiculous that people begun to engage in debates on whether or not there is evidence for ETs before they could articulate what it means to 'have an evidence of ETs' in the first place! Do some strange crop patterns prove that there are ETs? Does our failure to explain how a phenomenon was done on earth prove that ETs did it? Do dreams personal contacts prove that we are being contacted by ETs, or perhaps they are angels, gods, demons, or worse, just hallucinations? What is it that, a prior, constitute 'a prove that ETs are here'?
If you are in Arabia, and wake up one day and saw a stranger walking around in a strange vehicle, you cannot say 'this person must have come from outside Arabia'. You cannot tell where someone is comming from from how they look! You must, in some way, show the evidence that the person was at place x, outside Arabia, at one time, and now he is in Arabia. You must, for instance, show the photograph of the person in Egypt and then give it as the evidence that 'this person is a visitor from Egypt'. Otherwise you will just be making unsubstantiated assumptions about 'what type of people or things must they not be originating from Arabia'. You are blurring, for instance, what may as well be a discovery of 'unknown people native to Arabia'.
What is it about a saucer, that an object looking like that in the sky must originate from other planets? Before we can answer this question, a photograph or even direct experience of such an object in the sky does not prove anything about ETs! What is it unearthly about forming strange pattern on crops? How about being contacted by strange beings? How do you prove, for instance that some demons are not lieing to you that they come from stars? Perhaps they are invisible beings that dwells solely on earth and they know nothing about other stars. Of course people have expanded 'ET' concept to include what looks like the 'angels' or the 'demons' etc in the traditional religions. So what was the point of abandoning these religions? Of course in the bible, etc, the angels can go up there 'far beyond the stars' to 'where God is'. So if we ascribe 'magical' properties to ETs then we are winding up with the same old claims. So what is the difference between an ET and an angel? The only difference should be that the former is a 'physical' being in a physical planet that moves around using the technology they made rather than invorking 'the power of gods'. Granted, the technology may seem to be completely like a miracle. But the difference should be that the ETs worked with the technology using the knowledge they gained about the universe. An angel don't need to understand physics. He only needs a 'command of Yahweh' or someone like that.
So this lands us to one of the real 'evidences of ETs':
a)demonstrate the small scale version of the physics they use.
Long before people could go to moon, people could demonstrate the physics at work. People could shoot objects up, be it even over one meter high. So it remains to imagine that such a process, when 'scaled up' may eventually land man to moon. People could imagine such mileniums ago! So claiming that 'our technology is too limited' is not an excuse for not trying to figure out how an ET might fly. A demonstration of physics that can take someone to stars in split seconds will be a powefull evidence that ETs must be visiting us. It is the case that if there is a possible means of doing something, someone have probably already found out an actual way of doing it, and in the case of such a huge universe like ours, the probability uproaches certainity. Yes even in milky way alone. But if there is no such a means, the the multitudes of planets in the universe serve nothing to increase such a probability. It will be like adding a large number of zeroes with the hope of obtaining 1.
But perhaps you need a clue of how we can 'know' how to get to stars without being able to do it. It may be the case that we need to something as huge as a Dyson sphere to create 'portals' capable of taking people to stars. Such 'portals' may be demonstrated in small scales or in ways too dangerous. An example may be the fusion research. Of course scientists believe that an actual, controlled fusion plant is possible, even though we may not build one in centuries! A scientist will not have a hard time believing that some ETs might have already built a fusion power plant.
b)Demonstrate astronomical knowledge
Think carefully. If someone is in regular contact with ETs, we expect them to be an amazing fountain of knowledge about the universe. An ET from stars will of course have easily visted planets within solar system. Such a 'cosmic tourist' will have tremendous knowledge about the universe that he can share it with any vontactee. He could tell us of Comet Ison way before any scientist could detect! He could check if there is ort cloud etc. There is no reason why an ET should lecture us volumes of things about things on our own planet eg politics, how to go about our day to day life etc, in so called 'channeled messages', but tells us nothing about their own homes and other things that we cannot otherwise know. We don't need an ET to tell us 'love your neighbour'. We have more than enough humans to do that!
There is an interesting case involving the Dogon tribe, where they show some knowledge of the cosmos that is hard to explain how they obtain them. This is a good example I know of, but is still not 'predictive' enough. It is 'postdictive'. A predictive, Dogon-like knowledge of the universe, amongst the alleged ET contactees will be an evidence of reality of ETs worth millions of UFO photographs!