We're glad you asked! While the @ or "at sign" has seen a bit of a renaissance lately due to everyone's favorite 140 character or less social media service, it has actually been around for quite some time. Here in the Support Community, we're even making use of this little guy, although you might not know it yet!
Placing an @mention of another Support Community user not only lets them know you're talking to them, but also creates a link to their profile page! They're super easy to use, and handy as all get out. You can even use @mentions to create quick links back to content you've recently viewed, like so! Word Association
How can I get in on the @ction?
Just follow these simple steps to start slinging @mentions in the Support Community:
In a question or discussion, type the @ symbol and start typing someone's name.
An auto-complete box will help you complete the person's name.
You'll see their name next to a message icon like this: tmo_phillip.
Finish typing the rest of your question or discussion, and post!
Whoever you mention will now be notified, depending on their preferences.