The great depression of the 1920s saw human dislocation in the US reach an unprecedented scale. Hoboes travelled hundreds, sometimes thousands, of miles in search of work. As they did, they developed a glyphic language with which to share their experiences and collective knowledge.
A hash symbol (#) on a gatepost, for example, warned that it was the home of a policeman; steer clear. A rectangle around a dot indicated danger. If drawn above a wavy line it warned against dangerous water that should not be drunk.
Over the years the travelling community built up a letter-free language that would be immediately understood by their illiterate companions. It became a national language of signs and direction markers that ran parallel to the spelt-out signage of everyday life.
Almost 80 years on, this form of communication has been revived by hoboes of a very different kind: the travelling broadband generation.
It's less than a year since we first heard of 'wardriving', the practice of taking a notebook and wireless card out in a car and driving through a city in search of networks with unsecured wireless nodes. Then came 'warwalking' which was the same thing, but using a PDA and travelling by foot.
At the end of June this year, Matt Jones introduced the UK to the idea of 'warchalking' and, within a week, seemingly the whole world had caught on.
By combining simple icons with a couple of numbers and letters this modern-day hobo language effectively marks out fertile hunting ground for the mobile generation; unintentional Wifi hotspots where anyone with a notebook or PDA, and a wireless network card, can log on and browse the web for free. For the traveller, it's far cheaper than an hour in an internet cafe.
As an evolving standard it is still finding its feet, but its propagation is remarkable. Already the chief information officer for the State of Utah plans on using warchalking symbols on a more formal basis to mark out access points in some of the 250 buildings he administers.
Beyond sticking to the accepted signage conventions there seems to be only one hard and fast rule: as suggested by the name, you must use chalk.
This has nothing to do with the fact that it is less destructive than other forms of graffiti (one poster has already christened it 'wifiti'). It is in part due to the fact that the existing marks will get washed away, forcing their creators to remark them and check that they are still valid. Every rainstorm updates this chalk and brick database, and our city streets become a living map of free access to the online world.
For many companies the appearance of a warchalking glyph on the front of their building could be an embarrassment. How would clients of a legal firm feel if they knew that its networks were open to the world?
At the same time, though, it could serve to advise its systems department that something needs to be fixed. In this case, the very success of warchalking could be its downfall.
Hobo signs of the depression were poorly documented, and many have been lost over time. There is a fair chance, though, that they were passed from person to person among a closed group, much like Polari in 1960s Britain, thereby contributing in part to their longevity.
Warchalking, though, has literally exploded in a very short space of time, and the people who are likely to find it of interest are those who may be the focus of its attentions.
So, the system may die out before it has fully evolved, but there is another way in which it could, and should, survive. Its simplicity and independence of any national language makes it ideal for adoption anywhere in the world.
Whether it be a coffee shop in Seattle, a chip shop in Newcastle or an airport lounge in Hong Kong, any place that offers free wireless access to attract customers should be encouraged to adopt the conventions of warchalking to specify its network capabilities.
Like many international signs, the circular icons of warchalking will become the global language of the online population.