symbol vs marking

symbol and marking both are nouns.

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

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

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

symbol (noun)	marking (noun)
something visible that by association or convention represents something else that is invisible	evaluation of performance by assigning a grade or score
an arbitrary sign (written or printed) that has acquired a conventional significance	the act of making a visible mark on a surface
	a pattern of marks
	a distinguishing symbol