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A PNP transistor functions by allowing current to flow from the emitter to the collector when the base is held at a lower voltage than the emitter, which is typically connected to a positive supply voltage. When a sensor is energized, it often applies a low signal to the base of the PNP transistor.

In this scenario, with the sensor energized, the base of the PNP transistor is pulled down, allowing the transistor to conduct. As a result, the output at the collector side of the transistor is pulled high, responding to the energized state of the sensor. This leads to the output producing a high signal.

It's important to note that while a PNP transistor can theoretically output a variable signal depending on its operation conditions, the scenario described indicates a clear high signal when the sensor is active. Therefore, the correct characterization of a PNP transistor's output in this context is indeed a high signal.