sign manual vs signature

sign manual and signature both are nouns.

Word	Noun	Adjective	Verb	Adverb
sign manual	Yes	No	No	No
signature	Yes	No	No	No

As nouns, signature is a hypernym of sign manual; that is, signature is a word with a broader meaning than sign manual:

sign manual (noun)	signature (noun)
the signature of a sovereign on an official document	a distinguishing style
	your name written in your own handwriting
	a sheet with several pages printed on it; it folds to page size and is bound with other signatures to form a book
	the sharps or flats that follow the clef and indicate the key
	a melody used to identify a performer or a dance band or radio/tv program