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