key signature vs signature

key signature and signature both are nouns.

Word	Noun	Adjective	Verb	Adverb
key signature	Yes	No	No	No
signature	Yes	No	No	No

As nouns, key signature and signature are synonyms defined as:

key signature and signature: the sharps or flats that follow the clef and indicate the key

key signature (noun)	signature (noun)
the sharps or flats that follow the clef and indicate the key	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