Re: Other signs
Nuclear weapons while very unpleasant and destructive are quite puny compared to the average tropical storm. I read somewhere that they kick out more energy over a relatively short period than the entire world's nuclear aresenal. I don't know accurate that is, but the energy in these and electrical storms in immense.
By way of surviving artifacts from a civilisation? They would be few and far between on Earth and eventually almost all would disappear through plate tectonics if nothing earlier and more immediate such as the actions of plants and wind/water/ice.