First of all, if you were to have a gender identification for your characters, it would be best placed in the bio. And if it's in the bio, then why need a symbol when you could type it in?
But you want your gender to be instantly recognizable as some people do not bother with the bio.
If you were to have a symbol, it would be optional to portray for both you and everyone else - even if you have your symbol enabled it does not mean someone else can see it (they "can" but because you want this option for the sake of instant gender verification there's still a chance that someone else will not have this feature enabled and therefore their reaction won't be very instant).
But this optional symbol is the best way; something simple like an "m", "f", and "o", (at least) beside the character name, perhaps in a different colour to be easily differentiated from the name, would be ok. The same beside the username would be helpful too, if you want that. Of course, all of this could be turned off in the options menu for those who don't.
