In the rich text editor:
@CaptainYume
In a comment:
[CaptainYume](https://chowlings.com/user/CaptainYume)
For Names and Avatars:
In the rich text editor:
%CaptainYume
In a comment:
[](https://chowlings.com/user/CaptainYume) [CaptainYume](https://chowlings.com/user/CaptainYume)