I never catch an trans by eyes but I heard of the gaydar thing and for some reason I seams to have catch a few guys to be gay before they came out of the closet.
I where younger than now and I asked a older gay guy how he knew if someone was gay, he said it had alot to do with eye contact to spot another person, and then he said I should try to look at other men and see how they would look back and if a stranger could look me in the eyes for more than 10 second it ment they where attracted to me.
So I took a ride in the buss (should to school anyway) and tried it on random guys who passed by. most guys only looked shortly and then away, but there where one guys who looked back without turning his gaze away untill I looked away, and I notice when I stopped looking at him he still turned around to look at me once in a while..
theres also a saying that if a woman walks to you while keeping eye contact for more than 10 seconds and ask you about what time it is, do you really belive she want to know about the time?

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now this is only for attraction but in general I do belive eyes says alot.. when we are attracteed or drawn to someone/something our pupils gets bigger same as in darkness.
when we find something disgusting, fearfull, and so on our purpils get smaller, like in lightning..
maybe those facts are how you can notice if someone is trans.. like most guys who might find it disturbing to be compared with woman might get smaller purpils while mtfs would be drawn to it and get them bigger..
im just yapping.. sorry.. this just some of my thoughts..