One thing that puzzles me is how Stormtroopers can a) tell each other apart and b) know what rank each one is. They don't seem to have any rank insignia or identifying marks at all. Prior to the Empire the Clones had numerous colour and uniform variations which identify what type of unit they were part of but this was obviously dropped. Vader refers to one as Commander in ANH but how does he know which one of them is the Commander?

Please enlighten me!