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