The term BAT SIGNALS is a reference to the iconic signal used by Batman in the DC Comics universe. It is a bright light projected into the night sky, usually in the shape of a BAT, to summon Batman or other members of the BAT-Family. The crossword solution for this term is SONAR, which stands for Sound Navigation and Ranging. Sonar is a technology that uses sound waves to detect objects underwater, and is used by submarines and ships to navigate and detect obstacles.