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