Easter eggs have always been an integral part of the zombies mode in the Call of Duty series. However, we've also seen occasional easter eggs and secret achievements in the games' campaigns. Call of Duty: Modern Warfare 2 is no exception and it houses plenty of easter eggs and "side" ventures that you can embark on.
One of the side quests you can do is to find three hidden safes in two different missions. These are completely optional to go for, and opening all three rewards you with a secret achievement called 'Gentlemen Thief.'
Note that if you've already completed the missions, you can revisit them from the missions menu and leave the mission once you've opened the safe. It will still count towards the achievement.
Here are the locations of all three safes, along with their codes. We've also included a video guide for your visual reference.
Safe Location 1
The first safe can be found in the mission El Sin Nombre. It is in the bedroom across from Diego's office on the second floor.
Go inside the bedroom and see a painting on the wall to your left. The painting reads the name 'Lazar Salgado' with a date of 02/02/2019. As always, the date is the code.
Go further inside the room, and you will find a closed wardrobe across the bed. It is on the right side of the bathroom entrance.
Open the wardrobe, and you will see the safe.
Enter the code 02-02-19 to open it. You will find a Lockwood 300 shotgun and armor plate carrier.
Safe Location 2
The second safe is found in the mission Alone. You need to keep progressing through the mission until you come across a door that keeps "banging." When you open the door, a dead body will be on the ground.
Go through the door, and you will enter the coffee shop.
As soon as you enter, a locked door will be to your left.
Craft a pry tool, and open the door to access the room with the safe and the code.
The code is on the calendar. The calendar has highlighted a date which is 10th October 2020. Naturally, you would think that the code to the safe is 10-10-20. However, that is wrong.
You will also notice that the 10th date is highlighted with a circle and the number 40. The 40 represents the age of the individual. You need to subtract 40 from 2020, which leaves you with 1980. So the correct code to the safe is 10-10-80.
The safe is on the ground to the right of the desk.
Enter the code 10-10-80 to open and get a throwing knife and a .50 GS pistol.
Safe Location 3
The third and final safe is also in the same mission and relatively close by. Continue forward, and you will drop down to the ground floor of the coffee shop.
Take a left, and go to the end of the shop. You will find a window to your right.
Jump through the window and enter the garage next door. Make sure to take the back window and not the front door.
Once inside, go to your left. You will find a laptop on a desk inside the garage. The code is on the screen, and it is 37-60-80.
There is a small garage office right next to the desk with the laptop. Go inside, and you will find the safe.
Unlock the safe using the code, 37-60-80. You will get another throwing knife and a crossbow.
Once you open the third safe, you will get an achievement, 'Gentlemen Thief.'