@ (at sign)
The rise to prominence of Twitter from its launch in 2006 gave rise to using the at sign ("@") as a description for directing a public post to a particular user, especially for the purpose of replying to another user's post (i.e., "@janedoe"). Only after the usage of @ as a visual means of directing posts to specific users gained currency among Twitter users did Twitter developers begin to integrate the @ sign as a fundamental conversational tool on the site.[citation needed]
Initially, @ was used by Twitter users occasionally as shorthand for other words, such as location or time. The first person to use @ as a description of directing a post at another user was Robert S. Andersen ("rsa") on 2 November 2006;[1][self-published source] initially, this usage made use of a space between the @ and the name, followed by a colon and the main content.[citation needed]
The first to propose a general syntax for directly addressing users in posts were Ben Darlow[2] and Neil Crosby,[3][original research?] and by January 2007, more Twitter users began to take notice of the practice with various degrees of acceptance;[4][self-published source] within the year, the convention trended toward combining the @ and a Twitter username (as opposed to a real name) and prepending the combination to the beginning of a post in order to indicate a reply. Ultimately, they became colloquially known as "@replies" for their primary usage as replies to other users' posts. Twitter added support for "@replies" beginning in May 2008,[5][non-primary source needed] with any combination of @ with a username being turned into a hyperlink to the profile. On March 30, 2009, Twitter updated the feature and renamed it "Mentions" (i.e., to "mention" user "@janedoe") so as to include non-reply posts directed at individual users.[6][non-primary source needed]
Beginning September 2009, Facebook integrated the at sign as a mentioning feature; typing "@" in a post automatically initiates a drop-down autocomplete list containing names of "friends", groups and pages, which, after one being selected and the post published, links to the profile, group or page.[7]
@-replies started being used on Wikipedia around 2013.[8]
YouTube started introducing @-handles in late 2022.[9]
Distributed social networks and federated networks may use two at signs, the latter to indicate the instance/server which the mentioned users resides on. Example @[email protected] mentions the user janedoe on the server mastodon.social.
