Sign of ladies losing weight (4)
I believe the answer is:
omen
'sign' is the definition.
(omen is a kind of sign)
'ladies losing weight' is the wordplay.
'ladies' becomes 'women' (I've seen this before).
'losing' indicates named letters should be taken away.
'weight' becomes 'w'.
'women' with 'w' taken away is 'OMEN'.
'of' acts as a link.
(Other definitions for omen that I've seen before include "Augur" , "Sign of a future event, good or bad" , "Augury, portent" , "Sign of likely future event" , "Harbinger, prophetic sign" .)