In the rich text editor:
@CatHeadphones
In a comment:
[CatHeadphones](https://www.worldofgaia.org/user/CatHeadphones)
For Names and Avatars:
In the rich text editor:
%CatHeadphones
In a comment:
[![CatHeadphones's Avatar](https://www.worldofgaia.org/images/avatars/default.jpg)](https://www.worldofgaia.org/user/CatHeadphones) [CatHeadphones](https://www.worldofgaia.org/user/CatHeadphones)