signal vs foreshadow

signal is a noun but foreshadow is not a noun.

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

As verbs, foreshadow is a hyponym of signal; that is, foreshadow is a word with a more specific, narrower meaning than signal:

signal (noun)	foreshadow (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

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

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