Mojira mentions

Mojang Studios Note

You can tag other people using

[~username]

and replace username with the other user's username (not full name). These commands are determined by Atlassian that builds Jira, and nothing Mojang Studios can change.

In mojira, you can ping somebody with @.
But it's looking like it's only working half the times, and the developers like Ined seems to know how to use it
This is more a suggestion than a bug, but it'll be very helpful if a helpful text explaining how to mention somebody will be added at the main mojira page.