ringer vs signaller

ringer and signaller both are nouns.

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

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

Other hypernyms of ringer include signaler.

ringer (noun)	signaller (noun)
(horseshoes) the successful throw of a horseshoe or quoit so as to encircle a stake or peg	someone who communicates by signals
a contestant entered in a competition under false pretenses
a person who is almost identical to another
a person who rings church bells (as for summoning the congregation)