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