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