You thought the @ sign as a modern invention? From the computer age? Well here's an interesting bit of history on the origins and historical use of this ubiquitous symbol.
Why is @ on your computer keyboard?
The popular story that Ray Tomlinson saved @ from extinction by using it in email has spread as internet gossip. This story is false, and has been retold without people asking obvious questions like "Why was there an @ on Ray Tomlison's keyboard?"