Email us at email@example.com and put in the subject line "Signup Help."
Let us know your username so we can find your account and activate it.
Honestly do it early before you get frustrated and we can help expedite things.
Update 6/14/13: I have a waiting queue of 24,000 + new signups waiting for approval to start posting. 98% of them are spambots. Some of them are easy to weed out, alot of them are not. Unfortunately I can't always tell who's who and sometimes end up approving spambots and disapproving real people who want to join the community.
Myself and the rest of the community want to get as many real people to join this community as we can. Send an email to firstname.lastname@example.org and let us know that you are a real person and want to join our conversations. I'll be happy to approve you ASAP.