I'm one of those who'd welcome the idea of having a small gender icon under/in our postbits. You don't need to fill in anything if you don't want to reveal your gender right? But for those who want their gender to be known, it would be so much more convenient. And there are users who don't like to put the phrase 'aarinGirl/Guy' in their signatures..
Like simplyme said, why go over the lenght of writing something in your profile, joining aaringirls/guys groups, when a small icon could solve it?
I don't think it would do harm to anyone..