What type of show is the person entering? At least with my state's county fairs, the "animal id #" is a leg band attached to the bird. Chickens aren't registered like other types of animals, so they don't have paperwork, tattoos, etc. For means of identification, some shows just require that there be a leg band on the bird's leg, with an identification number on it. The identification # is recorded by the show secretary so that if the bird were to be stolen or something, there would be some way of recognizing it.
Most poultry shows that I've been to require no identification at all; I think it is mainly a county/local fair thing.