In the rich text editor:
@Hexy
In a comment:
[Hexy](https://painted-relics.com/user/Hexy)
For Names and Avatars:
In the rich text editor:
%Hexy
In a comment:
[](https://painted-relics.com/user/Hexy) [Hexy](https://painted-relics.com/user/Hexy)