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