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