I have looked at pictures of fully transitioned FTMs, and actual FTMs I know. There are 3 subtle things that IMO will "give them away" no matter how far past transition they are. (Not the Adam's apple thing like everyone says!) It's their small sized teeth, their hips in some cases, and their hands. That's been my experience. It's very subtle, but those seem to be the giveaways to me, if I see someone in public that makes me curious, and I am trying to figure out trans or bio-man, that's what I look for.