In the rich text editor:
@Lud_w1g
In a comment:
[Lud_w1g](https://chowlings.com/user/Lud_w1g)
For Names and Avatars:
In the rich text editor:
%Lud_w1g
In a comment:
[![Lud_w1g's Avatar](https://chowlings.com/images/avatars/default.jpg)](https://chowlings.com/user/Lud_w1g) [Lud_w1g](https://chowlings.com/user/Lud_w1g)