In order to apply for a badge, you must already have a valid Comic-Con Member ID or sign-up for one before February 12th.
From the site:
Everyone who intends to purchase, apply, or register for a Comic-Con badge must have a valid and confirmed Comic-Con Member ID. The Member ID site will close to new registrations and changes on February 12, 2013 and will not reopen before badge sales begin. This includes attendees, volunteers, professionals, trade professionals, exhibitor main contacts, and members of the press.If any of you Launchies are intending to attend Comic-Con this year to support Ender's Game, I suggest you sign up for a member ID as soon as possible. I wouldn't want anyone who wanted to go miss out because they forgot to register in time!
SDCC Member ID: Get one right now.