The Urban Legend of Alphabet Marks at the Front Door (The Door Code)
A House Marked With a Sign Had Become a Target
In the mid-2000s, strange posts began appearing on internet communities for homemakers and local mom cafés, often accompanied by eerie photos.
The story went like this. On the way home from work or school, someone happened to look beside their apartment doorbell and noticed a tiny, mysterious scribble that had never been there before.
"α, β, X, 👤... and numbers."

It seemed far too systematic to be a prank.
When they checked the next-door neighbor's entrance, a different symbol was written there, while the unit downstairs had no mark at all. As people online began analyzing the meaning of these symbols one by one, South Korea was swept into a vast wave of fear.
α (Alpha): A home where a man lives
β (Beta): A home where a woman lives
X: A home with a barking dog, or a home that is difficult to break into
Numbers (e.g., 1, 2): The number of residents, or the best time to visit
These were not traces left behind by ghosts. As rumors spread that they were "target markings" shared among real-life criminals, such as burglars or human trafficking rings, after completing their reconnaissance, the fear grew beyond control.