Sign in more than 50% of reading rooms (5)
I believe the answer is:
libra
'sign' is the definition.
(sign of the zodiac)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for libra that I've seen before include "House" , "Scales constellation" , "Person born under Scales sign" , "Someone born between September 23 and October 22" , "stars" .)