Sort of, but not really.
Right now, those devs with admin abilities on servers (read: not all of us, by a long shot) are able to hackishly use clan tags thanks to their admin powers. They started doing it because smurfs were becoming an issue -- folks were smurfing as devs, and we can't be having that. But none of the security measures that would need to go into clan tags -- things like clan registration, a leader's ability to change clan tags for everyone in his or her clan, the ability to toggle between teams you're on, some sort of user interface for it all -- all those things are still in the works. If we were to open it up right now, everyone would just be able to append or prepend whatever the hell they wanted to onto their names!
BUT! We're working on it. =)