Voice, bone structure, mannerisms/behaviors, taller than average height and build. The plastic surgery is supposed to help someone pass as the other physical sex, a finer nose or shaved brow or fake boobs shouldn't be a redlight that a woman is a man. My understanding of bottom surgery is that it's pretty passable. Not to mention the millions of women that get carved up by surgeon's scapels. We can see their surgery, too, but we still know they're women. You don't look at a transwoman and go "Oh shit, look at those plastic titties. That's a guy." That's just stupid. It's all context, my good fellow. Context.