wanted poster vs announcement

wanted poster and announcement both are nouns.

Word	Noun	Adjective	Verb	Adverb
wanted poster	Yes	No	No	No
announcement	Yes	No	No	No

As nouns, announcement is a hypernym of wanted poster; that is, announcement is a word with a broader meaning than wanted poster:

wanted poster: a public announcement by a law enforcement agency that they desire to question or arrest some person
announcement: a public statement containing information about an event that has happened or is going to happen

Other hypernyms of wanted poster include promulgation.

wanted poster (noun)	announcement (noun)
a public announcement by a law enforcement agency that they desire to question or arrest some person	a public statement containing information about an event that has happened or is going to happen
	a formal public statement