I think the main indicator of intelligent civilization would be burial sites and memorial monuments.
While 10s of millions of years of geological change would certainly make these hard to determine, an advanced civilization is likely to produce millions of these. Surely we would have come across some by now.
While 10s of millions of years of geological change would certainly make these hard to determine, an advanced civilization is likely to produce millions of these. Surely we would have come across some by now.