Gender roles! That's what these emojis represent. There are three of them here:
- Male. Used for boys, men, old men. Also it symbolises Mars.
- Female. Means girls, women, old ladies. As for planets, it's Venus.
- Male and female combined, represents transgenders.
There exist some names which are gender neutral, such as Max or Michele. In order to make it clear that you're male/female/still thinking, add a corresponding emoji to your nick.