Singers able to sign below (8)
I believe the answer is:
canaries
'singers' is the definition.
(I've seen this in another clue)
'able to sign below' is the wordplay.
'able' becomes 'can'.
'to sign' becomes 'Aries' (star sign).
'below' is a charade indicator (letters next to each other) (in a down clue, some letters go below others).
'can'+'aries'='CANARIES'
(Other definitions for canaries that I've seen before include "Mediterranean islands and yellow birds" , "Group of islands in the Atlantic" , "Yellow birds or islands off Africa" , "Yellow songbirds or Spanish islands off Africa" , "Small yellow finches" .)