Wow... this thread has gone all over.
To the OP: The brain is really, really good at figuring out all sorts of things by visual cues with regards to the face. We're constantly evaluating everyone around us through a set of learned behaviors that tell us things about the person whose face we're looking at. There are large areas of the brain both in the active cerebral cortex and the passive so-called 'reptilian brain' that are specifically tuned to tell things about the person in question. Now, all those impulses can be filtered through the conscious mind and have perspective bias buuuuut I'd wager that, properly trained, someone can tell various things about certain types of people.
To that, we all learn certain things about how to express ourselves through observation. Mannerisms, expressions, movement speeds, etc. are all learned through a process of appropriation as a child. The parent that we identify with gender (or maybe sex) wise is the one that we copy most thoroughly so, given that trans chicks are female and have some sort of auto-identification that makes that tick (though we don't become aware of it until about three or so, developmentally), I'd say that it's very possible to postulate a theory whereby ways in which we express ourselves using said learned behavior could be an indicator of gender (or as I'm going to start calling it: brain sex).
Add to that the fact that the eyes are the most visible sign of distress and turmoil and we've got a pretty easy little formula: feminine facial expressions + obvious signs of emotional distress = voila!
It doesn't always have to be 'woo' stuff, ya'll.
FWIW, my partner was pretty easily able to tell that I was trans by observing a lot of the same things. She wouldn't even call me 'handsome' pre transition, always opting to stay silent on the matter. When I asked her about it not too long before I popped, she told me that she couldn't see me as anything but 'beautiful' because there was something about my eyes that just didn't seem to be anything but.
