Nope! I'm sure that you don't have to announce the pace group you sign up for. I don't think anyone really "signs up" for a pace group. Pace groups are just there to help pace, and runners can even run ahead or behind of a pace group if they feel like it.
Edit:
Actually, after reading the Pace Groups link on the left: "The pace team is free for all registered participants and sign-up lists will be available at the Health, Fitness & Nutrition Expo."
I guess you DO sign up for a pace group. But I'm pretty sure you don't have to wear the time on your back if you don't want to. I don't think that you have to stay with your pace group that you signed up for, either.
But you should have someone who is actually organizing this race tell you all the correct information; as I'm just someone who's interested in pacing.
