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.
@ buzz – you broke your thumb and youre still twittering? that’s some serious devotion
— Robert Andersen (@rsa) …
Via: Mashable: Marketing