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