If it is determined that no risk of collision exists, what action is a vessel not required to take?

When it is determined that there is no risk of collision, the vessel is not required to reduce speed significantly because the regulations prioritize safety and navigation efficiency. If a vessel is on a steady course and has assessed the situation to conclude that the risk of collision is absent, there is no obligation to alter its current speed or make any drastic maneuvers that would unnecessarily disrupt the vessel's navigation.

In terms of the other options, maintaining a steady course is essential as it helps other vessels to predict your path, which aligns with the principles of safe navigation. Changing heading can be necessary depending on the circumstances and the intent to avoid potential hazards, while signaling to other vessels is important in maintaining communication and awareness between navigators, even when a risk of collision is not present. Thus, any of these actions may still be appropriate or advisable in certain situations, while a significant reduction of speed is not mandated under the assumption that there's no risk.