The Ssangmun-dong Police Department is a local police station in Ssangmun-dong, within the city of Seoul. It appears in "Hell".
After being released from the Squid Games, Seong Gi-hun visits the station to attempt to report the games and the deaths that occurred. This is dismissed as a prank or hoax, and the officers present refuse to investigate the matter seriously.
Gi-hun attempts to convince them by having them call the number on the Squid Game card he was given, but the number leads to a random woman. He is then kicked out of the police station, despite his protests. This is incidentally witnessed by a detective named Hwang Jun-ho.
When Jun-ho later goes to check in on his brother In-ho and finds a card in his apartment identical to the one Gi-hun presented. He returns to the police station the following day to ask the police officers there for Gi-hun's personal information in order to track him down.