When it comes to mail, we get a lot of post coming through the door that is unwanted - from bills we wish we didn't have to deal with, to take away menus and other spam.
But if you look closely at some of the letters you've been sent, you might notice some handwriting on the front or back that you didn't expect to find.
A Reddit user recently took to the online forum's Casual UK thread to ask for some help decoding what these symbols really mean.
They shared a photo of an envelope with the letter 'P' written on the front and circled.
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Their post read: "Can anybody tell me why all my letters the last few days have had a 'P' symbol written on them?"
Hundreds of people responded to the post to let the user know that it wasn't anything sinister.
In fact, it was just a simple way for their person delivering post to be super organised when out delivering mail, as the 'P' stands for parcel.
So it is to indicate that when they deliver your letter, they also have a parcel for you.
One person replied: "It means Parcel. For either yourself or the next delivery. It’s a reminder for the postman/postwoman."
Another, who works as a postman shared: "You had a packet/parcel. Stops us from forgetting about it!"
A third offered a slightly more detailed explanation, writing: "It's the postie's way of reminding themselves that when they come to post your letter there's also a parcel for you. That's so they don't post your letter then find out halfway down the street they forgot to knock and give you your parcel.
"Or sometimes they'll write P10 or something on the previous letter - that lets them know they have a parcel for next door (number 10) but no letter."
So there you have it folks! Mystery solved.
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