call number vs call mark

call number and call mark both are nouns.

Word	Noun	Adjective	Verb	Adverb
call number	Yes	No	No	No
call mark	Yes	No	No	No

As nouns, call number and call mark are synonyms defined as:

call number and call mark: a mark consisting of characters written on a book; used to indicate shelf location

Other synonyms of call number include pressmark.

call number (noun)	call mark (noun)
a mark consisting of characters written on a book; used to indicate shelf location	a mark consisting of characters written on a book; used to indicate shelf location