Definitely the admiring other girls figures and wishing that was me.
However, there are a few other big clues, no body hair, patchy facial hair from laser hair removal, two earring holes in each ear, long hair plucked eyebrows. long finger nails (although I keep breaking them!)
I'm suprised that others don't twig about my status daily. I reckon some people suspect but are too polite or scared to ask. If I am asked, I certainly intend to tell the truth.