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