I think it's a great idea. Not only does it make it easier for you to find your group, but it will make it easier for the teens to find each other. Children are always tuned in to find their parents. But as you know teenagers, they wander, they drift, they get caught in the gift shop, or have their noses in their cell phones...and when they turn around...it's easy to find the group if they know what to look for. I've seen many groups at WDW wearing brightly colored T-shirts and the group leader with a flag. Sure it seems geeky to everyone else, but it's better than calling Security to report a lost soul.