The sign for 'pound' (5)
I believe the answer is:
libra
I believe this is a double definition.
'the sign' is the first definition.
(sign of the zodiac)
'pound' is the second definition.
(I've seen this before)
'for' acts as a link.
(Other definitions for libra that I've seen before include "Person born under Scales sign" , "Zodiac sign of the scales" , "Balance constellation" , "Seventh sign of the Zodiac" , "Scales star sign" .)