The energy required to move at more than 10% of light speed makes an object moving at that speed easily detectable over very long distances just due to the collisions of the dust and gas in interstellar space with the ship. The radiation given off by those collisions will move at the speed of light ahead of said object and announce its arrival long before it gets here. We've had this detection capability for at least 60 years and have seen nothing.
IMHO, there are no spacefaring aliens.
Are we scanning the entire sky?
Are we looking for, and would we detect, said radiation headed towards where we will be when they get here[1]?
Even if the answer to both is yes, maybe they're just going somewhere else?
[1] One could argue that I should have used the word "there", not "here". If we take an earth-centric view of the universe, technically there (where an alien ship who wanted to visit earth at some point in the future would be heading) is not here, it's there. But, when they get there, there will be here (or here will be there?), so it's accurate to say either.