shoulder flash vs insignia

shoulder flash and insignia both are nouns.

Word	Noun	Adjective	Verb	Adverb
shoulder flash	Yes	No	No	No
insignia	Yes	No	No	No

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

shoulder flash: something worn on the shoulder of a military uniform as an emblem of a division etc.
insignia: a badge worn to show official position

shoulder flash (noun)	insignia (noun)
something worn on the shoulder of a military uniform as an emblem of a division etc.	a badge worn to show official position