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