The Mod Ogre: If I reply in black text, I'm just a poster; argue as you would with anyone else. When I reply under my Mod Name, or in red text (as I'm doing now), it is Mod Voice, and all that implies. I cannot recall ever doing Mod Name without red text, outside of a PM (and then it is usually "This is your first post, and you broke this local rule, so please pay attention and have fun); Black-text-with-mod-name is technically an option, but I don't do it.
If it's not red, it's no different than replying to anyone else on these forums (save Rich, obvs).