In the rich text editor:
@Avacard
In a comment:
[Avacard](https://chowlings.com/user/Avacard)
For Names and Avatars:
In the rich text editor:
%Avacard
In a comment:
[](https://chowlings.com/user/Avacard) [Avacard](https://chowlings.com/user/Avacard)