If I may ...
They are only "unidentified" until they land, or crash.
But maybe they are already here. Maybe, they are so advanced they don't fly, they just 'think' themselves here, and poof, they're here. Or maybe, just maybe, they're so advanced and smart thinkers, they poof themselves here and are flying around masked as normal airplanes? Kinda like what spies do with UPS trucks.
But of course we are not alone. With trillions of planets in the cosmos, all having been created out of the same materials, and elements, as our earth, there has to be some planet that coalesced such as ours with intelligent, human like life. However, since nothing can travel faster than the speed of light, that we know of, so far, and with any possible life sustaining planet, hundreds of thousands, or millions, or billions, of light years away, I'm pretty sure we won't see any visitors anytime soon. Especially seeing that humans, as far as we know so far, in modern form, being about 200,000 years young. And with our ancestors being only about six million years young. Nothing we humans have done, technologically, would ever reach the ears of interstellar intelligent life. In fact, we've been leaking radio signals, (radio signals travel at the speed of light), into space for over 100 years, but by the time they're 100 light-years away, they are so attenuated and weak, that they're basically undetectable anyway. Given the size of our own galaxy, the Milky Way, in which we reside, is roughly 110,000 light years in diameter? Well. We not on anyone's galactic tourist map.
One must also note, that the view from another galaxy, or universe, is completely different from how we view from earth. There is a whole lot to choose from out there in the expanse of things.
And, maybe, we aren't alone, if we 'think' we aren't alone. Maybe that's all it takes?