Great idea. Just a few thoughts to decrease the chance of an AP person cropping you out of the photo...
Judging by the tight shot here of Vaughn (so close that a big "imposter" type of sign wouldn't have shown up in the pic), you would need at least 2 people holding small and succinct signs in very bold ink. The more people the better, but these 2 people are key.
One person's sign should be held tightly behind her left shoulder and the other person's sign should be tightly behind her right shoulder. The two people should stick to her like glue so ANY photo that's taken of her will display at least one of the "Imposter" signs in the photo.
The idea is to make it impossible for someone to crop out your sign without destroying the photo's usability. Great thread, Kristann!
Kristinn.
(Sorry!)