If you watch the History, Discovery, Science channels, a few others, there’s been quite a lot of UFO sightings filmed. Some explainable, some not. One needs to keep in mind what UFO stands for, Unidentified or unexplained Flying Object. Along those same lines, you have USO’s. Unidentified/unexplainable submergible objects. The key words are unexplained or unidentifiable.
The government hasn’t been forthcoming on most of these leading to a ton of conspiracy theories. UFO doesn’t automatically mean ET or aliens. Although I believe that is possible. The Universe is so vast, consisting of billions of galaxies, I’m sure there is life out there, somewhere. That some of that life is intelligence life capable of space travel and perhaps beyond. Does that mean they’ve visited us at sometime in the past or present? Possible, but one can put their own probability equation or factor on that.
Every hear of the Fermi paradox? His reasoning goes like this:
There are billions of stars in the Milky Way similar to the Sun.[7][8]
With high probability, some of these stars have Earth-like planets in a circumstellar habitable zone.[9]
Many of these stars, and hence their planets, are much older than the Sun.[10][11] If Earth-like planets are typical, some may have developed intelligent life long ago.
Some of these civilizations may have developed interstellar travel, a step humans are investigating now.
Even at the slow pace of currently envisioned interstellar travel, the Milky Way galaxy could be completely traversed in a few million years.[12]
Since many of the Sun-like stars are billions of years older than the Sun, the Earth should have already been visited by extraterrestrial civilizations, or at least their probes.[13]
However, there is no convincing evidence that this has happened.[12]
https://en.wikipedia.org/wiki/Fermi_paradoxOr perhaps there’s ton of evidence of visitations, only we don’t know what we’re looking at or even for. There’s the possibility that the evidence is right in front of our eyes, but we don’t recognize it as such or don’t want to.