bell ringer vs signaller

bell ringer and signaller both are nouns.

Word	Noun	Adjective	Verb	Adverb
bell ringer	Yes	No	No	No
signaller	Yes	No	No	No

As nouns, signaller is a hypernym of bell ringer; that is, signaller is a word with a broader meaning than bell ringer:

bell ringer: a person who rings church bells (as for summoning the congregation)
signaller: someone who communicates by signals

Other hypernyms of bell ringer include signaler.

bell ringer (noun)	signaller (noun)
something that exactly succeeds in achieving its goal	someone who communicates by signals
someone who plays musical handbells
a person who rings church bells (as for summoning the congregation)