All any transsexual wants, really, is just to be accepted completely and without question just as any person is. It is very painful to be trapped in a body of the wrong sex. Almost all transsexuals have to suffer through some level of this until they finally become more or less 'passable'. Until their bodies and faces change to the point nobody gives them a second glance. Some people never are so lucky, and are forever not 'quite good enough'.
People can kinda tell.
Then they live for the rest of their lives in a kind of hell. After years of study, after being TS myself, I can tell. You go though something, you know it. I would never tell anyone though. If you do, ask not how you 'can tell' if someone is transsexual.