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