signature vs melodic line

signature and melodic line both are nouns.

Word	Noun	Adjective	Verb	Adverb
signature	Yes	No	No	No
melodic line	Yes	No	No	No

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

signature: a melody used to identify a performer or a dance band or radio/tv program
melodic line: a succession of notes forming a distinctive sequence

Other hypernyms of signature include air, line, melodic phrase, melody, strain, tune.

signature (noun)	melodic line (noun)
a distinguishing style	a succession of notes forming a distinctive sequence
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