From the Romans to Twitter, the hash sign – or octothorpe – has had a rich history, and now this innocuous little character has found a mighty resurgence as the hashtag. What happened along the way?

Can't find the hashtag key on your Mac or MacBook keyboard? Here's how to type the # special character on a Mac. The hash symbol – also known as the pound/number sign, or even the octothorp(e) as ...