Final answer:
Seeing both sidelights of another vessel indicates a crossing situation, which requires specific navigational actions to prevent collisions at sea.
Step-by-step explanation:
The question seems to be related to navigational rules for vessels at sea, more specifically, understanding the lights seen on other vessels and what they signify about the situation between two ships. When you see both sidelights of another vessel, it is a sign that you are in a situation where paths intersect, typically known as a crossing situation. In such a situation, navigational rules prescribe certain actions to prevent collisions, such as altering course to pass astern of the other vessel if you are the give-way craft, or maintaining course and speed if you are the stand-on craft.