Going to http://beta.worldofwarcraft.com redirects you to http://beta.worldofwarcraft.com/game/character-copy.html.... You are not presented by a beta signup page though. But, instead of "error not found" you'll get a "403 Forbidden" text.
This is pretty interesting since prior to the announcement of Wrath of the Lich King, http://www.worldofwarcraft.com/wrath/ gave you the same result: "403 Forbidden". People speculated this would be the now announced expansions website address, and they were right.
It might be the case that it's the same this time and that Wrath of the Lich King will enter beta testing soon. This is just a rumor, though! Just know that this very URL did not give the same error message previously, instead it said "not found".
Either way, it's definitely interesting.