What signal would a vessel aground show during daylight?

A vessel that is aground during daylight visibility would display three black balls as a distress signal. This signaling practice is established under the Inland Navigation Rules for vessels that are not able to maneuver or navigate due to being grounded. The use of three black balls is specifically designated to alert other vessels to the fact that assistance may be needed, indicating that the vessel is not under control, which is critical information for nearby ships. Displaying this signal effectively communicates the situation to others, promoting safety and preventing potential accidents or collisions in the area.

The other options do not correctly represent the required signaling methods for a vessel aground. One black ball is used for a vessel that is stationary and not under power, while two black diamonds indicate that a vessel is engaged in fishing. A black square is not used in the context of a distressed vessel. The three black balls remain the internationally recognized method for indicating a vessel aground during the day.