A decade ago it was little more than a curiosity at the bottom right-hand corner of the telephone keypad, quietly fulfilling its primary function of providing a bit of company for the zero key. There was little consensus on what to call it; in the US it was the pound, while others called it the cross, hex, square, or number sign. These days, however, a whole new responsibility sits on the shoulders of these four intersecting lines.
Across Twitter, Instagram, Tumblr, Google+, and soon (if rumours are to be believed) Facebook, the hashtag is supposed to help us cope with the information deluge by serving as a categorising symbol, a tagging device. Click on #kittens, and you should see kittens. Click on #m11, and you might discover information about the current state of a motorway running through Essex. But hashtags have strayed way beyond the internet. They now appear on billboards, television show titles and product packaging; if you're brave enough to watch MTV's Geordie Shore you'll hear the word "hashtag" dropped into casual conversation, while Ed Miliband's recent response to the Budget in the House of Commons featured the clumsy phrase "hashtag downgraded Chancellor". We're in the middle of a hashtag epidemic. But what purpose, if any, do they serve?
User-experience designer Chris Messina had big dreams for it. Back in August 2007 he tweeted to his followers: "how do you feel about using # (pound) for groups?", and in doing so unwittingly kickstarted the phenomenon. The # sign was already used to signify groups or topics on the online communication platform IRC, but it took time for Messina's idea to percolate through Twitter. The tipping point coming in 2009. Early that year the #followfriday tag became a convenient way of telling people about new and interesting people to follow; June saw hashtags become a tool of citizen journalism during the protests following the Iranian election, and in July Twitter linked all hashtags to a search page containing tweets featuring that tag. This was a pivotal moment; it brought clarity to how hashtags could and should be used, but also demonstrated their chaotic, ad-hoc nature.
Anyone can create a hashtag, and anyone can use that hashtag in any context. So they can't be controlled; they're used to bring order, but they can easily create disorder in equal measure. The prospect of grabbing attention on social media, however, is a temptation that brands can't resist, and they've embraced the erratic hashtag with a passion. "'Engagement' has become the holy grail for advertisers," says Katy Lindemann, a freelance strategic planner. "It's a largely meaningless term, but it's usually a melée of different metrics that are used as a proxy for 'paid some kind of attention to our thing'."
But there have been many instances where brands have tried to get people to "join the conversation" and failed. When, in 2009, a social-media underling working for Habitat decided to advertise £2,000 gift cards tagged #mousavi (the name of the Iranian opposition leader), there was an immediate outcry. But others found themselves following in Habitat's footsteps; the roll call of disastrous trips into hashtag land includes such respected names as McDonald's, Qantas, Vodafone and, um, Hertfordshire Police.