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