One of the common functions of Facebook and Twitter is the ability to mention or tag people in your status or tweet. Just as you can do this with an '@' symbol on those social sites, you can do the same here on GeoNet. This allows you to link places or content, or even mention a person you would like to join the conversation.
How to mention
Once you begin typing after the '@' symbol, a list of possible options will display. You can use an underscore (_) for spaces.
The powerful thing about GeoNet is that not only can you mention people, but you can mention places and content. For example typing @ArcGIS_Online returns several options such as ArcGIS Online and Routing in ArcGIS Online.
Even if you are not sure of the exact wording you can type the words in any order.
What happens when you mention
When you mention a person they are notified in their Inbox and based upon their preferences they will get an email as well.
When you mention a place, the mention will show up in the activity stream of that place and people following that place will be notified of the mention.
Learn more about Using @mention