abbreviation vs signifier

abbreviation and signifier both are nouns.

Word	Noun	Adjective	Verb	Adverb
abbreviation	Yes	No	No	No
signifier	Yes	No	No	No

As nouns, signifier is a hypernym of abbreviation; that is, signifier is a word with a broader meaning than abbreviation:

abbreviation: a shortened form of a word or phrase
signifier: the phonological or orthographic sound or appearance of a word that can be used to describe or identify something

Other hypernyms of abbreviation include descriptor, form, word form.

abbreviation (noun)	signifier (noun)
shortening something by omitting parts of it	the phonological or orthographic sound or appearance of a word that can be used to describe or identify something
a shortened form of a word or phrase