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The meaning of a bizarre symbol that can be found on buildings across the has been revealed. The symbol, an engraved arrow pointing to a horizontal line, is commonly found on private buildings.

Chris Spargo posted a video on TikTok to explain the meaning behind the symbol. He has around 13,000 followers on the platform and offers answers to "the small questions" in his posts. He revealed that the symbols were installed by the in the 19th century.

According to Chris, there are at least 100,000 of the symbols, known as Ordnance Survey Bench Marks (BMs), across the nation. They are used to record heights above sea level.

Chris explained: "They're called Bench Marks. No one knows exactly how many of them there are, but we know it's at least 100,000 and it might be as many as half a million.

"If you're in the UK, no matter how remote you are, you do have one of these hidden in plain sight around you right now. They were installed by Ordnance Survey, Britain's national mapping agency, starting in the 19th century.

"Back then, if you wanted to know the difference in elevation between this town and the next one, there were very sophisticated tools that would allow you to measure that but you would have to go out and work it out yourself, because no one else had done it for you."

The Bench Marks were used to create accurate maps of land heights. They offered a clear fixed point of height and were used as a point of reference while railway networks were built.

Chris continued: "As we started to build things like railways, it was becoming pretty important to know the differences in elevation across the country. So the Ordnance Survey went out and spent two decades mapping out lines across Great Britain and Ireland, measuring the differences in elevation along the way.

"At every point they measured, they left one of these (symbols). And once they were done, each of those Bench Marks became a new reference point that could be used to fill in the rest of the country."

While some Bench Marks are found on public property, others are on private buildings. They can also be found on structures like kerb stones or even boulders.

Chris added: "If you look at Ordnance Survey maps from the 19th century, you'll see these Bench Marks everywhere. So now if you wanted to know the height of a particular point, all you had to do was measure it relative to the nearest Bench Mark.

"Then you'd instantly know its height relative to every other part of the country. A lot of these symbols are on the side of private buildings because the Ordnance Survey Act of 1841 had given them the right to enter private property and do what they needed to do."