In the rich text editor:
@Lawnmower
In a comment:
[Lawnmower](https://chowlings.com/user/Lawnmower)
For Names and Avatars:
In the rich text editor:
%Lawnmower
In a comment:
[![Lawnmower's Avatar](https://chowlings.com/images/avatars/1496.png?v=1656251359)](https://chowlings.com/user/Lawnmower) [Lawnmower](https://chowlings.com/user/Lawnmower)