An answering machine signal is a sound or tone that one hears when they make a call and the line is not picked up by the other party. There are several synonyms for this term. One of them is voicemail signal. This refers to the tone or sound that plays when the call is not answered and goes straight to voicemail. Another synonym for answering machine signal is call tone. This is the sound that one hears when the phone is ringing and is used to alert the person that there is an incoming call. Lastly, some people refer to answering machine signals as message tones as they are the sounds that indicate the presence of a message being left by the caller.