El Sin Nombre is the 11th mission in Call of Duty: Modern Warfare 2. Although you are not required to open Diego’s safe in order to complete the mission, doing so will contribute to the Gentleman Thief trophy/achievement. Inside the safe are a plate carrier and a Lockwood 300 shotgun.
Where to find the code to Diego’s safe
Turn left as soon as you enter Diego’s room and look at the painting above the small cupboard. It’s a portrait of Lazar Salgado with the date 02/02/2019 written on it. The code to Diego’s safe is 02-02-19.
In the middle of the room, there is a closet with a safe. Unlock it to get a plate carrier and a Lockwood 300 shotgun.