After playing Resident Evil 3 Remake for a while, you'll find yourself playing the part of Carlos as he tries to make his way through the police station. There is a chest here that you can open to get a very useful upgrade in the form of more inventory space.
To find the safe, you will first need to go to the west office. Go left from where you entered the building, into a room with a safe that you will need to open with a key card you got from a dead policeman outside.
There is a door at the end of the room which leads to a long hallway. Take it down, take out the zombies along the way. Go to the operations room and search around it to grab any items you can find. Proceed to the next area and get ready to take out a lot of zombies. When they are all down, you can head to the west office and you will find the safe in a small room next to it.
The code for the door is Left 9, Right 15, Left 7. Opening it will give you a hip pocket and 2 additional inventory slots.
If you're curious where the current code is, you'll need to exit the West Office, then turn right down the hallway until you reach a staircase with a door below. Go ahead and you will find a memo with the code that mentions the location of the safe and the code to open it.