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