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