signal

any communication that encodes a message

• “signals from the boat suddenly stopped”

any incitement to action

• “he awaited the signal to start”
• “the victory was a signal for wild celebration”

an electric quantity (voltage or current or field strength) whose modulation represents coded information about the source from which it comes

communicate silently and non-verbally by signals or signs

• “He signed his disapproval with a dismissive hand gesture”
• “The diner signaled the waiters to bring the menu”

be a signal for or a symptom of

• “These symptoms indicate a serious illness”
• “Her behavior points to a severe neurosis”
• “The economic indicators signal that the euro is undervalued”

notably out of the ordinary

• “the year saw one signal triumph for the Labour party”