What act is typically indicated by black or green smoke?

The act typically indicated by black or green smoke is firing a torpedo. Black smoke is often associated with the discharge of a torpedo, as it can denote the use of specific propulsion systems that produce this kind of smoke. Historically, vessels engaging in naval warfare would use smoke as a visual signal to indicate their actions or state. In contrast, green smoke generally signifies a tactical or operational procedure related to torpedo use.

Furthermore, other options do not align with the smoke signals being discussed. Emergency signaling generally employs different colors or methods, such as flares or flags, instead of smoke. Ship grounding would not usually create distinct colored smoke visible from a distance. Likewise, the act of a man overboard is typically communicated through distress signals or flags rather than smoke.