An alien species, capable of interstellar travel, would probably have sensors good enough to locate a number of artifacts in space in and around the solar system (remember Voyager 1 and Voyager 2, at least, are in the process of leaving the solar system), as well as some on the Moon. In vacuum conditions these should be identifiable for millions of years.

A careful examination of the fossil record and the distribution of species around the planet, would also reveal an era (in geological terms extremely brief) of unusually rapid long distance migrations of plants and animals; as well as the mass extinction). This is evidence independent of the direct discovery of fossil humans and human artifacts.

I suspect all these strands of evidence would be diagnostic of an intelligent species which was not wise enough to avoid global catastrophe.

Of course, as the ultimate technological fix, we might have downloaded our minds to machines or created artificial intelligences as our successors; so the aliens could get a first hand account of what happened.