Every time a GM bans one, another one pops up. To me this seems like the only logical way to prevent it. My suggestion is to filter it from appearing to other users, similar to the way other servers have censored certain words (I wouldn't go as far as them, but gold selling sites seem reasonable to block). Ideally, I'd suggest making it so that the text goes threw on the client that sends it but no one else for best effectiveness.
Additionally, if you like this idea, you might want to per-emptively filter URL shorteners since that will likely be next route they take.