portend vs signal

portend is not a noun while signal is a noun.

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

As verbs, signal is a hypernym of portend; that is, signal is a word with a broader meaning than portend:

Other hypernyms of portend include bespeak, betoken, indicate, point.

portend (noun)	signal (noun)
	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

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

portend (verb)	signal (verb)
indicate, as with a sign or an omen	communicate silently and non-verbally by signals or signs
	be a signal for or a symptom of