emblem vs red flag

emblem and red flag both are nouns.

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

As nouns, red flag is a hyponym of emblem; that is, red flag is a word with a more specific, narrower meaning than emblem:

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