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