Apply for TAG? Sign for TAG? lol, funny..
I was so stress out about same thing last year and guess what? You don't even need to do any of those crap. Simply, read their terms and conditions then check the TAG box during UC application period, and you are set. You don't need to meet with counselor or anything.
*Scenario above applied to UCSD ONLY. For UCSB, you have to sign a contract with your counselor ;p