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Phoenix666 [soylentnews.org] writes:

“Inspector Sands to the control room, please [bbc.com].” If you ever hear that at a British train station, don’t panic. But you might appreciate knowing that this is a codeword meant to inform staff that there is an emergency somewhere in the building [wikipedia.org]. The idea is to avoid causing alarm among commuters, but still get the message out to those trained to deal with the problem.
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Not all codes are alphanumeric. Some are visual, intended to be hidden in plain sight. As BBC Future discovered earlier this year, many banknotes feature a specific pattern of dots [bbc.com] called the EURion constellation, placed there to prevent people from photocopying money. Many copiers and scanners are programmed to spot it.

Other visual codes are scrawled in the landscape around us. One surprising example is the series of signs known as “hoboglyphs [weburbanist.com]” – a collection of symbols meant to provide information to travelling workers and homeless people. Among other things, these could indicate the quality of a nearby water source, or suggest whether the occupant of a house is friendly or not.
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And finally, the spray-painted squiggles [bbc.co.uk] you see on pavements in towns and cities all over the world adhere to codes understood by construction workers and engineers. A BBC News Magazine report recently revealed the meaning of many of these in the UK, and pointed out that different colours related to different types of cable or pipe. Blue meant a water system while yellow indicated gas lines and green labelled CCTV or data wiring.

They forgot to mention the secret masonic codes.

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