On the right wall of Line 4, there is a marker. Additionally, a marker can be found in Line 6. The marker actually exists in Line 1 as well, but it's not visible. The last marker is on Line 9, but it's not within the surveillance. Instead, it's on a cabinet in the control room. At this point, two possible passwords can be obtained: 4169 or 4119. Enter each of these sets of numbers on the controller and then press the power button to activate the surveillance; one of these sets is correct.