The term 'kind of signal' can refer to a variety of different signals, such as sonar (5 letters), SMOKE (5 letters), BUSY (4 letters), TURN (4 letters), and goahead (7 letters). Sonar is a type of signal used by ships and submarines to detect objects underwater. SMOKE signals are a form of communication used by Native Americans to send messages over long distances. BUSY signals are heard when someone is already on the phone. TURN signals are used by drivers to indicate when they are turning. Goahead signals are used in telecommunications to indicate that a message has been received and the sender is ready to receive a response.