A subspace signal was a quick signal through subspace to attempt to initiate communication or to check for responsiveness. In 2369, Odo and Croden were in the USS Ganges when a subspace signal came in on the Vulcan band frequency. It was a communication from the captain of the T'Vran asking if the runabout needed assistance. (DS9: "Vortex") Later that year, Benjamin Sisko proposed using a class-2 probe to investigate a narrow band subspace signal emanating from a moon in the Gamma Quadrant. (DS9: "Battle Lines")