There was one poster that I respected and assumed was male. One day, they posted links to feminist blog posts that they had obviously book-marked (They were not recent). I am not saying men can't read feminist blogs (I do myself on occasion); but from that point on, I "read" them as female.
Why didn't you ask him/her? It's not creepy to ask somebody's gender, especially when most of you guys aren't that pervy after all. Seriously
most of you guys have been super nice and polite to me

I thought of that. I decided it really was not important; since they are not really a dating prospect. I try to avoid mentioning my own gender.
BTW, this was one of the links mentioned:
Five Reasons You Need to Break Your Emoticon Addiction. (I guess I am going to be read as female now by shy people like me

)
Not a dating prospect, why not? If you're single n looking for a bf/gf it could happen anywhere, anytime, you never know. Good luck!