Meaning

noun any nonverbal action or gesture that encodes a message

noun any incitement to action

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

originFrom Old French segnal, seignal or Medieval Latin signāle; noun use of the neuter of Late Latin signālis, from Latin signum; verb use from 1805, as a shortened from signalize (1650s). Doublet of signum and sign.

Etymology from Wiktionary, CC BY-SA 3.0