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