‘How the @-Mention Took Over Social Networks’ – ‘Mashable’

Seth Fiegerman says, “The “@” symbol used to be just for email. Then it was for Twitter too. Now, it transcends networks.In 2006, Robert Andersen, then a freelance designer who later joined Square as a founding team member, became the first person on Twitter to use the “@” symbol to reply to another user. Andersen didn’t do a proper @-mention as we know it today — a space separated the symbol and the username — but it helped establish a language for communicating that is now commonplace on Twitter“.