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