You've probably seen those big yellow "H" signs attached on lampposts before. In fact, you most likely pass them several times a day without noticing.
But it turns out that while they are very common, a lot of people have no clue what they're for.
While you may not give them a second thought, it turns out these signs play an important role in saving lives, as they help firefighters locate an important resource.
South Yorkshire Fire and Rescue Service have taken to social media to reveal the importance of the markers - and their explanation has left people shocked.
In a video posted to TikTok, the Yorkshire-based fire service wrote: "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."
The photograph displayed in the short video tells firefighters that there's a 100mm water main 10 metres away - leaving people completely flabbergasted by the explanation, reports Chronicle Live.
"I never knew. Everyday is a school day thank you," one TikTok user wrote, while another, added: "Well I learnt something new today thank you!"
A third added: "I’ve never even seen one of these signs never mind know what it means," while a fourth commented: "Good to know. Thank you for sharing."
"I used to think it was H for helicopter landing," one user admitted - with others in agreement. "I thought it was a helicopter landing pad," a second said, with a third echoing: "thought it was H for helicopters".
Last week social media users were gobsmacked to learn the origin of the term blockbuster. A TikTok star shared a video that detailed the word's origin.
The word is so synonymous that the popular but now defunct video rental store named itself after the term - but many don't know the word's historic meaning.
Alice James, 30, shared where it came from - leaving people stunned as many admitted that they had no idea where it originated.
Taking to TikTok, where she uploads as @alicekjames, Alice said: "Are you ready to have your mind absolutely blown? I learnt what the term 'blockbuster' meant the other day and I haven't stopped thinking about it. It comes from the fact that in the olden days if a movie was a blockbuster it meant the line went around the block to buy tickets."
Alice's video soon went viral and had over 150,000 views alongside countless comments.
One viewer admitted: "I didn't know this either and I'm 59."
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