Which visual signal can be used to indicate distress by day?

The square flag with a ball above it is an internationally recognized distress signal used during the daytime. This signal is known as the "November" flag, which consists of a square blue flag with a ball above it, commonly referred to in maritime contexts as a signal for requesting assistance. When displayed, it conveys an urgent message to nearby vessels that the displaying vessel is in distress and needs help.

This visual distress signal is prominent and easily identifiable, making it effective for alerting other vessels in the vicinity to the situation requiring attention. Its standardization ensures that mariners across different regions understand its meaning, which is crucial for safety at sea. The use of this flag aligns with international maritime regulations, ensuring a consistent approach to signaling distress across various vessels and situations.