Alot of Forums and Messaging Clients have them, a notificating/bumping feature.

It's a good Feature allowing to tag specific Users, to make sure they read the message without actually beeing subscribed to the thread.

For example writing the Name of a User with a "@" infront of it, makes the Message become a link to his Profile and a message appears in his User Control Panel that he has been "bumped" in this thread :

@ShhhMikes

To make sure this is not abuseable by just entering every User you can find without any reason, a rule that specifys to only use this Feature with a Reason should be introduced.