There are numerous secondary sexual characteristics that, when taken together, allow highly reliable sex differentiation.
- face shape
- breasts or lack of
- crotch bulge caused by male genitalia
- adam's apple only found in males
- hip-shoulder ratio
- hip-waist ratio
- brow ridges in males
- torso length to limb length ratio
- hand size
- foot size
- facial hair
- hairline at forehead
- voice pitch
- gait
I'll grant that cross-sex hormones and surgery can mask some of these, but some cannot be masked, creating a noticably disjointed appearance in someone on cross-sex hormones. A transman with broad hips, no adam's apple, and no brow ridges will jar visually even after testosterone has caused facial hair growth. Place your hand over a photograph of Buck Angel from the nose down and look at Buck's eyes and forehead. They are unmistakably female, even now.
This visual jarring attracts attention subconsciously in the viewer, even if they cannot identify the cause. I've sometimes looked several times at someone "odd-looking" trying to figure out why, then they've moved or spoken and I've realised that they are on cross-sex hormones.
The whole point of a lesbian-only club is that it is for homosexual adult female humans only. By definition, that excludes anyone male and anyone heterosexual. It wouldn't be a lesbian-only club if it were "inclusive".
I was sexually assaulted aged eight by two older boys who used my secondary sexual characteristics of breast buds and hip-shoulder ratio to determine that I had a vulva that they could touch without my consent. I know this because they agreed a tactic of "you keep her there and I'll touch her fanny" immediately prior to the assault, as well discussing how my pubic hair felt during the assault. The idea that they didn't know that I had a "fanny" and touched me to determine whether I had one or not is ridiculous and the idea that a lesbian would do that to other women is not only absurd, it's highly offensive.