I've read that two faces of a coin are named H and T but I don't know for what words they stand. Do You know the extended forms?
and the head is - as you'd expect - the side with someone's head on it. I've never seen a tail depicted though - a thistle, a portcullis, anything really.
b PS I have a feeling that numismatists use fancier words. Perhaps 'face' (for head, and 'obverse' (for tail). I'm sure Wikipedia would tell you if you ask nicely...)