I've sometimes wondered if Venus' runaway greenhouse had been caused (presumably unintentionally) by intelligent Venusians in the distant past, how could we fin

I've sometimes wondered if Venus' runaway greenhouse had been caused (presumably unintentionally) by intelligent Venusians in the distant past, how could we find out? What bio- or techno-signatures would we still be able to find? And what possible such signatures would be easiest to look for given the inhospitable conditions?