Have we looked for human-like signals in the geological record?
Any nuclear activity would be visible in the changes of the isotope ratios far longer than the existence of our Universe. Nothing was found until now, except one in Gabon. It was natural phenomenon: at the time, 2billion years ago, there was far more ${}^{235} \rm U$ and the ground water could moderate uranium ore, if it was enough rich.
Except that, nothing was found until now.
Offtopic, but the case is same for radio signals. If any Earth-like civilization would exist in 100 light years away, we would see their radio signals. There is radio silence.