The correct answer is C) letter K in Morse code given by light. The signal to guide vessels in distress, indicating "This is the best place to land," is the letter K in Morse code, given by light. This is the standard signal used by the U.S. Coast Guard and other maritime authorities to direct distressed vessels to a safe landing spot. The other options, while potentially signaling distress in some contexts, do not specifically indicate the best landing location as the Morse code K does.