Signal Oscar Tango is a radio transmission in the vicinity of Jury Street Metro station. The large antenna tower near the station entrance can be turned on after unlocking the gate. Once the power is restored, it begins broadcasting Morse code. Judging by the morse code translation, the message is actually asking if anyone is nearby as if the sender were asking "Is anybody out there?"
The nearby drainage chamber is accessed through a manhole cover in the middle of the road (under the crosshair in the photo to the right), due north of the tower. The chamber includes the broadcasting ham radio, a Big Book of Science, a pre-War book, two stimpaks, a motorcycle gas tank, a motorcycle handbrake and several other small items, including a rare gum drops by the knocked down shelves.
Opposite the radio on the chamber's east wall is an electrical switch which opens the sleeping chamber below. Inside are several bodies mutilated by raiders. As you are inside the chamber, two raiders may enter the chamber above you, which means you have to fight your way out.
The station transmits:
|-.-. --.-||CQ||Calling anyone|
|--- -||OT||Oscar Tango|
|--- -||OT||(The operator's|
|--- -||OT||call sign)|
So overall it says: "Calling anyone this is Oscar Tango over". Basically, "over" is actually saying "I am awaiting reply".