Krikkiter,
Thank you for your questions. For those who only accept verifiable physical scientific proof as evidence, there is no evidence. However the definition of evidence includes observation, which therefore includes eyewitness accounts.
So if we accept eyewitness accounts as evidence, we have plenty of evidence to suggest that UFOs ( alien craft ) are extraterrestrial, but still nothing direct. In other words, I know of no UFO witnesses who claim to have observed a UFO coming into the Earth/Moon system. But such observation is possible and it has been rumored to have been accomplished by space monitoring stations at Space Command. But rumors are not evidence.
Consequently, for evidence of extraterrestrial visitation, we are left only with eyewitness accounts that suggest that what was seen was something that no Earthly technology was capable of manufacturing at the time, and therefore was probably manufactured by extraterrestrials.
Given the lack of verifiable scientific evidence that proves alien visitation has happened, it is natural for many people to be highly skeptical. It is also reasonable for people who have never seen a UFO ( alien craft ) to simply reserve judgement pending convincing evidence or an experience of their own. Certainly there is also a lot of misinformation and hoaxes on the Internet.
Until we acquire some hard evidence, the best evidence for you to personally seek out is to start asking people if they have ever seen a UFO and listen to their accounts with an open but skeptical mind. If you do this enough times, you will come to realize that the UFO mystery is not as cut and dried as the critics on this forum would lead you to believe.