To be easiest to identify the gender of a poster, it would be nice if the colored spot or whatever, showed up beside their posts. sort of like: name, bpnet veteran, avatar picture, join date, location, gender, number of posts, etc.
However, it might be easier to add to the site on the profile page, under "additional information". At least it would be there for those who cared to take the time to go looking.
I think this would be a great addition, as long as sharing the information was optional.
Oh yeah, and before I posted using the word "gender", I looked it up in an online dictionary. The definition of being synonymous with "sex" was listed before the one about traits associated with a particular sex. So nothing wrong with using the word gender here.