What does a distress signal by day consist of?

A distress signal by day is primarily recognized through visual means, which includes the use of flags or shapes that indicate an emergency situation. The correct answer points to the internationally recognized practice of using visual symbols to convey distress signals effectively.

During daylight, one prominent method prescribed for signaling distress is the use of a flag shape, typically a square or ball, that can be easily identified from a distance. This visual signal can be understood universally by those who might assist, regardless of language barriers. The clear geometric representations help ensure that the signal is visible and discernible in various environments.

While other options involve communicating emergency situations, such as Morse code or sound signals, they are more relevant to nighttime or other specific circumstances rather than daylight. Thus, the use of visual signals, particularly in distinctive shapes like a square or ball, is the standard for indicating distress during the day, making this answer the right choice.