Final answer:
The indication of an engaged autothrottle system in aircraft typically appears as a message on the display screen, not a green light, audible alarm, or flashing red light.
Step-by-step explanation:
The indication that the autothrottle system (ATS) is engaged typically includes a message on the display screen of the aircraft's cockpit. When the autothrottle is activated to manage the power settings of an aircraft's engines, the specific indicators can vary depending on the aircraft make and model. Usually, on commercial jetliners, this is displayed as a mode enunciation on the Primary Flight Display (PFD) or on the flight mode annunciator panel. An audible alarm or flashing red light is generally indicative of a warning or critical condition, whereas the use of green lights or messages on the display screens convey normal operation, which includes autothrottle engagement.