The hash symbol: the secrets of the symbol made famous by Twitter

The hash symbol: the secrets of the symbol made famous by Twitter

Eugenia Luchetta Published on 3/5/2021

Although many people call the ubiquitous # symbol a ‘hashtag’, the hash symbol or key is actually just part of a hashtag, which also includes the words that follow it.

This grid-shaped symbol has many different names, and it has had an equally large number of functions over the centuries in the English-speaking world, and later in the rest of the world too. In the UK we call it the hash symbol (derived from ‘cross-hatching’ – shading using angled parallel lines), while the Americans call it the number sign or pound sign, but the technical term for it is actually an octothorpe. And then there are a whole host of unofficial names referring to its shape, such as ‘square’, ‘grid’, ‘fence’, ‘crunch’, and so on.

From L to R: Akzidenz Grotesk, Big Caslon and Fago. There is little variety in the design of the hash symbol in various typefaces. It almost never has serifs, and the only things that change are the angle of the stems, which are very often of equal weight, and the distance between them.

The history of the hash symbol’s names is intertwined with the various things it has been used to represent. And the one that came first was definitely ‘pound sign’.

A unit of measurement

It was neither social media nor the telephone that created the hash symbol. As with so many other things, its origins lie in Latin.

It is impossible to work out when the symbol we know today first appeared, but we know that it derives from the Latin term libra pondo, i.e. ‘weight in pounds’. The word ‘pound’ stems from pondo, meaning ‘weight’, and has been abbreviated as lb since the 1300s. As early as the seventeenth century, printers were producing specific movable type for this glyph.

An excerpt from ‘Pyrosophia’ (1698) by Johann Conrad Barchusen showing the lb symbol with a perpendicular dash, indicating an abbreviation. Courtesy of the Roy G. Neville Historical Chemical Library, CHF.

The evolution of the lb symbol into the hash symbol as we know it today comes from handwriting. Although it is unclear when the current version became official, it seems that over time, as it was jotted down more and more quickly, lb slowly transformed into #.

A barred lb symbol drawn by Isaac Newton. Courtesy of the Chemical Heritage Foundation Collections.

This is where the name pound sign came from, as well as its use as a unit of measurement. And this function led to another American custom: using the # to mean ‘number’, i.e. the number sign, still today common as an alternative to the abbreviation “No.”

An obscure button (and name)

Although most people have never heard of it, let alone used it, the technical term for the # symbol is octothorpe. But where does this absurd, difficult-to-pronounce word come from?

To find out, we need to go back to the 1960s, and to the offices of Bell Laboratories, the renowned telecommunications company, still going strong, which produced the first telephones. Researchers at the company were modifying the telephone keyboard to allow for some new functions, and they added two new buttons next to the zero, which needed to be given appropriate symbols. After some research and various different attempts, they decided to use the asterisk and the hash symbol, which were already found in the ASCII code and so were already familiar to many users. The next job was to give a name to the symbols, and particularly to # – the name ‘pound sign’ was no good, as it could be confused with the symbol for the British currency. And so, over a cup of coffee, they came up with the name ‘octothorpe’, derived from the prefix octo-, indicating the symbol’s eight points, and a second term with a less clear origin, which has given rise to a series of anecdotes. The most likely theory is that it derives from the Olympic athlete Jim Thorpe, whose medals were taken off him because he had played basketball at a professional level. It seems that the Bell employee who chose the name was a fan of his.

1966, model 1500 telephone, Bell Labs. One of the first models to include the symbols * and #.

The hash symbol on the telephone keypad was used for a few specific commands, but, a bit like the name octothorpe, it remained mostly unused by the average user. Nevertheless, despite lacking a true meaning, the hash symbol became familiar to the general public.


The person who gave # a real role was Chris Messina, the man who is considered the inventor of the hashtag

Messina, an expert on social media and forms of digital interaction, suggested that Twitter should start using hashtags – a word preceded by a # – to group, categorise and index discussions. Hashtags actually already existed: they appeared for the first time on the internet in the Internet Relay Chat (IRC), a network where users could communicate within various channels, with the subject identified by a hashtag. It was within this community that the name ‘hashtag’ was first coined.

Messina’s suggestion was initially met with scepticism by Twitter’s founders, who thought it would make interacting too ‘nerdy’. Nevertheless, hashtags began to circulate on Twitter and grew in popularity. In 2008, during his election campaign, Obama launched the hashtag #askobama. The following year Twitter responded, introducing the hyperlink function to hashtags, which allowed users to search for tweets using a specific hashtag. At this point the use of hashtags by users increased dramatically, and over the next three years the symbol also appeared on YouTube, Tumblr, LinkedIn, Instagram and Facebook.

Needless to say, hashtags created a completely new form of communication, particularly in the field of marketing.

Similarly to what happened with other symbols, the creation of hashtags gave # a new lease of life, and turned it into an ultra-recognisable symbol full of meaning for the general public. Just like @, Messina chose # because he wanted to use a symbol that was already in circulation rather than inventing something new, which would have made it more difficult to understand and less likely to be adopted.

As technology is developing ever more quickly and is continually altering our behaviour and the ways we interact, what other symbols currently gathering dust in front of our eyes on our keyboards will come back to life and become part of our everyday existence?

Sources: Keith Houston. “Shady Characters: The Secret Life of Punctuation, Symbols, and Other Typographical Marks” (2013).