hash mark vs hashmark

hash mark and hashmark both are nouns.

Word	Noun	Adjective	Verb	Adverb
hash mark	Yes	No	No	No
hashmark	Yes	No	No	No

As nouns, hash mark and hashmark are synonyms defined as:

Other synonyms of hash mark include service stripe.

hash mark (noun)	hashmark (noun)
an insignia worn to indicate years of service	an insignia worn to indicate years of service