What is universally recognized as an international distress signal?

The internationally recognized distress signal is flying the National Ensign upside down. This action indicates a situation of extreme emergency or distress, typically used by a vessel in peril. When the flag is displayed in this manner, it communicates to other vessels and nearby individuals that help is urgently needed. This signal has historical significance in maritime operations and is standardized by international maritime laws, making it easily recognizable regardless of location or language barriers.

The other options do not have the same universal recognition as distress signals. Firing a warning shot can be context-specific and may not clearly indicate an emergency requiring assistance. Flashing a light signal, while useful in communication, does not define a distress situation as clearly as the inverted flag. Displaying a red flag might indicate danger or restricted activities but is not universally accepted as a signal of distress.