Does anyone know the episode where there was a guy who drew what looked like an atomic symbol but it represented different cliques?
I don't know, sorry, but I might be able to narrow it down - I don't think this was on the Vegas CSI..
I spent about an hour looking for this, and even briefly checked Criminal Minds, but I couldn't find anything. I don't think it was on Vegas either. I haven't watched the spin offs closely.
There was a series 1 episode of CSI Vegas where a security guard was being over helpful with the CSI's and I do vaguely remember him writing a bomb equation on the wall. But I'm not sure whether this was what you were on about. The Episode in question is Season 1 Episode 13: Boom.