red flag vs emblem

red flag and emblem both are nouns.

Word	Noun	Adjective	Verb	Adverb
red flag	Yes	No	No	No
emblem	Yes	No	No	No

As nouns, emblem is a hypernym of red flag; that is, emblem is a word with a broader meaning than red flag:

Other hypernyms of red flag include allegory.

red flag (noun)	emblem (noun)
something that irritates or demands immediate action	special design or visual object representing a quality, type, group, etc.
a flag that serves as a warning signal	a visible symbol representing an abstract idea
the emblem of socialist revolution