In the rich text editor:
@Gem4567
In a comment:
[Gem4567](https://chowlings.com/user/Gem4567)
For Names and Avatars:
In the rich text editor:
%Gem4567
In a comment:
[![Gem4567's Avatar](https://chowlings.com/images/avatars/default.jpg)](https://chowlings.com/user/Gem4567) [Gem4567](https://chowlings.com/user/Gem4567)