A possible answer from the Merck Vet Manual:
"Mycoplasma gallisepticum infection is commonly designated as chronic respiratory disease in chickens and as infectious sinusitis in turkeys...In chickens, infection may be inapparent or result in varying degrees of respiratory distress, with slight to marked rales, difficulty breathing, coughing, and/or sneezing. Morbidity is high and mortality low in uncomplicated cases. Nasal discharge and frothiness about the eyes may be present. In turkeys, the disease is generally more severe than in chickens, and swelling of the paranasal sinus is common. Feed efficiency and weight gains are reduced. Broilers and market turkeys may suffer high condemnations at processing due to airsacculitis."
My personal point of view is that these turkeys should NOT go to the fair even if you see symptoms subside or disappear in time. You don't want to risk passing on a potentially devastating chronic respiratory disease (or any type of disease for that matter) to another person's birds - just as you wouldn't want them to do that to you. Besides, I'm sure you would only want to show your healthiest, best looking turkeys since you're not only trying to show off excellent examples of the breed, but also of your turkey husbandry skills. Right?