Sign that's reversed in dollar bills (5)
I believe the answer is:
libra
'sign' is the definition.
(sign of the zodiac)
'reversed in dollar bills' is the wordplay.
'reversed' says the letters should be written backwards.
'in' indicates a hidden word.
'arbil' is hidden in the letters of 'dollar bills'.
'arbil' backwards is 'LIBRA'.
'that's' acts as a link.
(Other definitions for libra that I've seen before include "Person born under Scales sign" , "Old pound" , "The Scales in astrology" , "Scales constellation" , "Balance constellation" .)