I suspect any evidence short of multiple artifacts from multiple locations would be circumstantial at best, regardless if the traces are in the planet's geologi

I suspect any evidence short of multiple artifacts from multiple locations would be circumstantial at best, regardless if the traces are in the planet's geological record or in the genetic code of an ancestor of whatever the supposed ancient ones ate for dinner. On the other hand, multiple correlating indicators could give a pointer about where to look. Alas, it's likely such a place either deep underneath the ocean floor or that it's buried under kilometres of rock.