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