On the internet? In general I take someone that spells "God" with a capital to be a theist (usually only 2 of 3 monotheistic believes, because Muslims usually use "Allah" probably). Or perhaps raised as a theist, lost their faith, but not bitter against their old faith. while if someone uses "god" they are probably not a theist.
Makes sense to me too: I as a theist would refer to "Thor" as a "god" because to me it is not an entity that exists. It would only make sense for someone that is an atheist to not use a capital to refer to my "God": They don't believe it to be a real entity after all.
E: although, I guess fictional characters do use capitals, so maybe I'm wrong.
My thoughts