I wouldn't think those would be noticeable unless you were already closely observing the earth.

I'm not a physicist, but I assume there isn't any detectable, unique signature of an explosion that can be detected from space. Stories I've read about test-ban treaties and non-proliferation efforts give the main mechanism for detecting tests are the seismic effects they have.

What sort of signals do (human scale) nuclear explosions give off that are detectable from light-years away?