A sign of love, to males (4)
I believe the answer is:
omen
'a sign' is the definition.
(omen is a kind of sign)
'love to males' is the wordplay.
'love' becomes 'o' (love means zero in tennis).
'to males' becomes 'men' (man is a kind of male).
'o'+'men'='OMEN'
'of' acts as a link.
(Other definitions for omen that I've seen before include "Augury, portent" , "Harbinger, prophetic sign" , "Foreboding" , "Event regarded as a prophetic sign of good or evil" , "Harbinger, augury" .)