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