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