Supervisor's Note is a written note found in Death of the Outsider.
The front gate code is [three digit number]. I can't stay here a minute longer. For a while it was just the little flashes of light, like cracks in a windowpane, but now? I hear voices. And it's not just a few whispers! Whole conversations, like they're right beside me. Sometimes I see strange people out of the corner of my eye, but then they're gone. It's like everything shivers and changes in front of me and then it's back to normal, like nothing happened.
This place is cursed. I don't know what's going on, but I'm not waiting for it to get worse. I'm going back to Karnaca.
This note can be found in the top left room of the warehouse by the gate, during the mission A Hole in the World.