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