visual signal vs signal

visual signal and signal both are nouns.

Word	Noun	Adjective	Verb	Adverb
visual signal	Yes	No	No	No
signal	Yes	Yes	Yes	No

As nouns, signal is a hypernym of visual signal; that is, signal is a word with a broader meaning than visual signal:

Other hypernyms of visual signal include sign, signaling, signalling.

visual signal (noun)	signal (noun)
a signal that involves visual communication	any nonverbal action or gesture that encodes a message
	any incitement to action
	an electric quantity (voltage or current or field strength) whose modulation represents coded information about the source from which it comes

visual signal (adjective)	signal (adjective)
	notably out of the ordinary

visual signal (verb)	signal (verb)
	communicate silently and non-verbally by signals or signs
	be a signal for or a symptom of