It seems a tad excessive to jump on people for a sign-off -especially one that is clearly well-meant. People sometimes say 'God bless you' to me and I reply either "Live long and prosper' or 'May the Force be with you'. If they get snarky about it, I know they aren't real Christians. If they look blank, I know they aren't real nerds. In either case I probably won't speak to them again. If they smile or laugh, then they're genuine in one or both ways, and so fine by me.