You've probably walked past them hundred of times, but do you know what the yellow signs with the 'H' on them on lampposts mean?
What are the two numbers at the top and bottom for? Is this important information we've somehow missed?
People had all sorts of theories about what the H stands for.
"Thought it was H for helicopters," one TikToker said, one of several people who seemed to think helicopters had a habit of landing on residential streets.
"Oh dear, not me thinking hospital close by," another said.
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"It’s nowt to do with me so I just walk on by. What do I need to know for?" a third commented. Pragmatic, I like it.
Ready to find out what the H signs actually means?
South Yorkshire Fire posted a video on TikTok, saying: "POV: You’ve walked past these small yellow signs your whole life.
"But it was today you realised, finally, after all these years, they are there to tell firefighters where the hydrants are."
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Yup, the big Hs are to show fire crews the location of a water supply, as sometimes the fire hydrant cover is obscured.
Some people were adamant that they’d always known, saying they’d been taught at school or that it was simply ‘pretty obvious’.
But many others admitted it was brand new information, with one saying: "I never knew. Everyday is a school day thank you."
Someone else said: “Well I learnt something new today thank you!"
Some TikTokers also asked what the numbers meant above and below the H.
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According to Hydrants Direct, a company that maintains and tests privately owned fire hydrants, local authority fire and rescue services are usually responsible for the hydrant signs.
The website explains: "The location of a fire hydrant is indicated by an above ground post or marker plate.
"Hydrant marker plates are rectangular yellow signs, with a large black H and a pair of numbers, usually attached to a wall, lamp post or a short concrete post. The two numbers on the plate show the size of the water main and the approximate distance of the hydrant from the plate. Yellow paint is sometimes used to help identify a fire hydrant cover.
"As well as marker plates, all hydrants are also shown on the digital maps available in fire engines, so that the nearest one can be found while firefighters are on their way to an incident.
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"This also means that even if marker plates are missing or broken, the fire service will still be able to find them in most cases, and once reported they will be repaired in due course."
Simon Fearn