See sign showing decay (6)
I believe the answer is:
caries
'decay' is the definition.
(dental caries)
'see sign' is the wordplay.
'see' becomes 'c' (the word for the letter, according to Chambers).
'sign' becomes 'Aries' (star sign).
'c'+'aries'='CARIES'
'showing' is the link.
(Other definitions for caries that I've seen before include "I scare easily with tooth decay" , "Decay in bones or teeth (6)" , "Dental decay" , "Decayed area in a tooth" , "Decay of bone or teeth" .)