Signal

noun

1. sign, indication
2. an act, event, or watchword that has been agreed on as the occasion of concerted action
3. something that incites to action
4. something (such as a sound, gesture, or object) that conveys notice or warning
5. an object used to transmit or convey information beyond the range of human voice
6. the sound or image conveyed in telegraphy, telephony, radio, radar, or television
7. a detectable physical quantity or impulse (such as a voltage, current, or magnetic field strength) by which messages or information can be transmitted