You dont check. This isnt about perfection, its about preventing unnecessary exploitation of 'rights'. You are physically of a certain genitalia, you use the facilities designated for that. If a transgender who identifies as female will primarily dress as one just as a one that identifies as male wouldnt be questioned. If they are civil and minding their own business, shouldnt be a problem. Besides, restrooms have stalls. Its when you have no standards whatsoever that it becomes a major problem. In the case of open showers and even locker rooms where people undress in front of others, one can easily see that no designation would be ripe for exploitation for peeping toms, impostors or perverts, no? Tootsie?