An octothorpe is the pound sign, but it is sometimes called the number sign. Britain, however, knows it as the hash sign. Social media addicts know it as a hashtag since its usage began in 2007 to introduce metadata tags on posts to various social media platforms. The symbol itself probably goes back to Roman times, with the term libra pondo, meaning pound weight. The abbreviation for libra pondo contained two vertical strokes topped with a horizontal as to not to have the symbol confused with the number 1. Users in the United States know the symbol # as the pound sign, but outside of the states, the pound sign is known as the symbol used to denote the British pound currency.