" You have unlocked " but I don't know what it is.

[mezb]

After I did Clemente Hotel (Sins of the Father) Rank S my game says
You have unlocked Forgotten

I check all the clothes, watches, etc on customization and didn't find anything called Forgotten. There was another rank S I did a search on the customizations items and didn't find either.

Is it a department area ?

[Bluehawk]

It's a tattoo.

[SkebbZ]

All S ranks unlock a tattoo for the respective map. Some maps also unlock something else, but every single S rank gives a tattoo.

[mezb]

Thank you guys, the tattoo was the only thing I didn't check.