In the rich text editor:
@Hex_77
In a comment:
[Hex_77](https://www.worldofgaia.org/user/Hex_77)
For Names and Avatars:
In the rich text editor:
%Hex_77
In a comment:
[](https://www.worldofgaia.org/user/Hex_77) [Hex_77](https://www.worldofgaia.org/user/Hex_77)