I can say yes, I can definitively tell if someone is trans... especially if they are trying to pass as male and are not on T. My friend/co-workers and cousins were able to spot trans people too. When I was at a concert with my friend years ago, this was before I came out to him(actually that night driving back home is when I told him I was trans)Anyways, we were hanging around waiting to go into the concert, and my friend turns to me and says, "that's a girl? I thought she was a boy until I heard her talk". Another time was at work and and a few of my co-workers who knew I was trans were talking about another ftm saying, "I think this person is trans", ftm, and I looked and sure enough, I believe they were. Though, I never talked to the two trans people at work when they were there. I felt they were more masculine than me and that intimidated me. But then again, I'm a very shy person so I won't go up to people and start talking to them. I also went to a trans/parent meeting that my counselor set up and I was able to tell who the trans people were from the voice and height and there was only one other trans guy there besides me. The other was a trans woman. To me, for ftm's, the voice is a dead give away and he started his transition in the early 90's. I mean he looked and sounded male and everything, but the voice and height was such a give away to me. Though, my grandmother couldn't tell b/c I asked her if she could tell if he was trans or not and she said no she couldn't tell. But being trans, it was a dead give away for me. I could tell so easily by the voice it's self and the height.