What does a blue and white alpha flag signifies?

A blue and white alpha flag, often referred to as the "Alpha" flag in maritime signal flags, signifies that a vessel is either "diving" or has a diver down and requests that other vessels keep clear of the area. The flag is part of the International Code of Signals used to communicate important messages at sea. Displaying this flag helps ensure the safety of divers in the water by alerting nearby boats to exercise caution.