The are our own.
Well, I hope the really cool ones are.
The demons can keep the clunky, silly-looking ones.
And you know that for a fact, right?
UFOs could be one of the following: 1) ships from the future—ie time machines. 2) ships from other mirror dementions more advanced than we are. 3) Ships from some as yet unknown civilization here on Earth, like from the sea floor, Poles, Inner Earth? 4) Ships from the Moon. 5) Ships from hold out Nazis from WW II just waiting to return. 6) Ancient Gods? 7) Demons from hades. 8) Angels from God? OR 9) creatures from other worlds.