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