symbol vs marker

symbol and marker both are nouns.

Word	Noun	Adjective	Verb	Adverb
symbol	Yes	No	No	No
marker	Yes	No	No	No

As nouns, marker is a hyponym of symbol; that is, marker is a word with a more specific, narrower meaning than symbol:

symbol: an arbitrary sign (written or printed) that has acquired a conventional significance
marker: a distinguishing symbol

symbol (noun)	marker (noun)
something visible that by association or convention represents something else that is invisible	some conspicuous object used to distinguish or mark something
an arbitrary sign (written or printed) that has acquired a conventional significance	a writing implement for making a mark
	a distinguishing symbol