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