Since the first time I saw you say you're female, you've been female.
Sure, irregulars might not know but those who simply recognise your name and have seen you post that you're female, just know.
Many screen names on tech forums, albeit inadvertently - appear male. So when one of those names turns round and says "Well actually, I'm female", it tends to stick.
I dont think it should be mandatory, but if there's something that helps go for it. But if it means that much, I think signature is a great place to put it. Thats making an effort. Its a shame you only get one per page.
On a more facetious note, anyone remember "ASL"? We could append that to our sn's.
SUroot-32-M-UK