Facebook users can now tag their friends, Pages, Groups, and Events in comments to news feed stories and wall posts to create linked mentions. This will help users carry on conversations with other commenters and allow them to easily reference different entities on Facebook.

In September 2009, users gained the ability to mention friends and other Facebook pages in their status updates and wall posts by typing an “@” symbol followed by the first letters of a name and then selecting from a drop-down menu.
Later Facebook began showing tag suggestions whenever a user capitalized a letter in an update or post, but later removed the feature since it interrupted users who weren’t actually trying to tag anything.
Now users can type an “@” symbol to initiate the tag drop-down menu in comments. Until this release, some users had taken to manually typing @[first name] without it properly linking in order to create unofficial mentions in comments.
When a user is tagged, they’ll receive an notification stating that a friend “mentioned you in a comment.”

The new comment mentions also create new opportunity for Pages. Admins can “Use Facebook as Page”
In September 2009, users gained the ability to mention friends and other Facebook pages in their status updates and wall posts by typing an “@” symbol followed by the first letters of a name and then selecting from a drop-down menu.
Later Facebook began showing tag suggestions whenever a user capitalized a letter in an update or post, but later removed the feature since it interrupted users who weren’t actually trying to tag anything.
Now users can type an “@” symbol to initiate the tag drop-down menu in comments. Until this release, some users had taken to manually typing @[first name] without it properly linking in order to create unofficial mentions in comments.
When a user is tagged, they’ll receive an notification stating that a friend “mentioned you in a comment.”
The new comment mentions also create new opportunity for Pages. Admins can “Use Facebook as Page”