hallmark vs assay-mark

hallmark and assay-mark both are nouns.

Word	Noun	Adjective	Verb	Adverb
hallmark	Yes	No	No	No
assay-mark	Yes	No	No	No

As nouns, hallmark and assay-mark are synonyms defined as:

hallmark and assay-mark: a mark on an article of trade to indicate its origin and authenticity

Other synonyms of hallmark include authentication.

hallmark (noun)	assay-mark (noun)
a distinctive characteristic or attribute of someone or something	a mark on an article of trade to indicate its origin and authenticity
a mark on an article of trade to indicate its origin and authenticity