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