As a previous poster says, how the fuck do you know? They could have a beard, wear hobnailed boots, there is no criteria.
You have zero way of knowing.
But also how would you know if they're Sagittarius, or have a degree, or like Formula One, or enjoy knitting.
Nothing absolutely fucking nothing, precludes a man from saying he's a woman.
Look at Alex, a stonewall representative. Full beard, totally male. Apparently brings out the inner 'lesbian' in his girlfriend
Or these men. One is a man one is a woman, one is, er, neither.