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