shoulder mark vs epaulette

shoulder mark and epaulette both are nouns.

Word	Noun	Adjective	Verb	Adverb
shoulder mark	Yes	No	No	No
epaulette	Yes	No	No	No

As nouns, epaulette is a hypernym of shoulder mark; that is, epaulette is a word with a broader meaning than shoulder mark:

shoulder mark: epaulets that indicate rank
epaulette: adornment consisting of an ornamental cloth pad worn on the shoulder

Other hypernyms of shoulder mark include epaulet.

shoulder mark (noun)	epaulette (noun)
epaulets that indicate rank	adornment consisting of an ornamental cloth pad worn on the shoulder