Fascinating pictorgraphs used by train-hopping nomads warning each other of dangers ahead and flagging 'kind' people susceptible to begging are still in use today and are posted on signs and left on walls across America.

The late 1800s growth of the American rail system, coupled with economic downturns in later years, led to a rise in the number of hobos — nomad migrant workers or homeless travelers — hitching illegal rides on freight trains.

By the early 1900s, it's said that there were more than 500,000 hobos in the US.

The 'hobo code' was a series of pictographs used by hobos are they travel around the US, catching illegal rides on freight trains beginning in the late 1800s

Hobos used the symbols to inform each other about helpful locals or of dangers ahead

To help each other out in their cross-country travels, these hobos developed a system of pictographs and occasional words and phrases which turned into the 'hobo code.'

The codes were chalked, carved or otherwise written in conspicuous places near the tracks for other hobos to see and frequently included helpful hints about directional information, warnings about what was up ahead and also information about people who would be willing to help a hobo out with things like food, medical treatment and work.

By the early 1900s, there were said to be more than 500,000 hobos traveling the rails

According to the code, a drawing of a cat indicated that a kind woman lived in the hours, while a cross mean that hobos could expect to receive food at the end of a sermon and shovels revealed that work was available.

Meanwhile, circles and arrows would indicate directions hobos were better off traveling in.

The pictographs were chosen because they didn't require hobos to be literate to understand or draw them, plus they were sufficiently obscure enough that they'd be ignored by anyone who didn't know the code, according to 99% Invisible.

News reports of the time appeared to exaggerate the widespread use of the hobo code pictographs, though, likely because hobos were the ones talking about their codes and, as a group, they tended to be fond of embellishing the truth, according to Vox.

In the 1910s, famed hobo Leon Ray Livingston — AKA 'A-No. 1' or 'The Rambler' — made the rounds by highlighting both the hobo lifestyle and the hobo code drawings in interviews and books he wrote, such as 1911's Hobo Camp Fire and 1914's The Ways of the Hobo.

A chart showing the extensive topics the hobo codes provided information about

Examples of the hobo code shown on display at the National Cryptologic Museum

Hobo code pictographs are still in use today. These symbols written near the New Orleans Ferry on the Mississippi River are said to indicate 'OK' and 'good way to go'

Examples of the hobo code graffiti are still being discovered today, despite the fact that they were generally designed to be temporary and often written in grease pencil or chalk.

Anthropologist and Pitzer College professor Susan Phillips came across some excellent examples of hobo code graffiti, as it's now called, in 2000, under a bridge near the Los Angeles River, when she found chalkings featuring about 20 names attached to dates which went all the way back to 1914.

'Being able to look at this wall that was still intact and completely untouched by any contemporary graffiti, it was absolutely remarkable that it survived,' Phillips told CityLab.

A century later, the hobo code continues to capture the imagination of people.

The concept of the hobo code was incorporated into an episode of Mad Men in 2007 (shown)

In the episode, a hobo can be seen chalking the sign for 'dishonest man within' on a post

Florida artist Patrick Stickney has created a series of paintings incorporating hobo code marks

In 2007, TV series Mad Men centered an episode around the concept, naturally titled The Hobo Code, during which one character shows another character various pictographs and what they mean.

Meanwhile, artist Patrick Stickney has created a series of paintings he's titled Hobo Hieroglyphics, which are on display at the New Port Richey, Florida's Pasco Fine Arts Council through November 10.

In the series, Stickney showcases the hobo code pictographs by painting them over brilliantly colored scenes.

Stickney first saw examples of the hobo code glyphs when he was riding a bike on an Erie Canal bridge in the 1950s, according to the Tampa Bay Times.

'As an artist and art historian I've have [sic] always been fascinated by these symbols - a wonderful form of communication, and a creative, unique form of American art,' Stickney said in a statement.

The hobo code tradition continues in the present day, but are now digitally enhanced since hobos now have access to cell phones and computers.

Website including DumpsterMap.com and WiFiFreeSpot.com exist to point towards opportunities for finding food and free Wi-Fi hotspots.

'Prior to 2005 or so, all of this was simply done word-of-mouth, which is how it was done for over 100 years,' a hobo called Huck told Newsweek in 2015.

However, modern day hobos are still hoping to keep the written hobo code alive and are working towards creating new symbols to represent the availability of things like Wi-Fi and free power outlets.

Like their rail-hopping ancestors, these new codes are being designed to be obscure.

'The codes are for us,' Huck said, noting that 'if other people see it, they could have clues to our secrets, and the next thing you know, that outlet that was accessible to hobos is now locked up or completely gone.'