Sign of some nepotism (4)
I believe the answer is:
omen
'sign' is the definition.
(I've seen this before)
'of some nepotism' is the wordplay.
'of' says the answer is hidden in the clue.
'OMEN' can be found hidden inside 'some nepotism'.
(Other definitions for omen that I've seen before include "Sign of likely future event" , "Augur" , "Harbinger, portent" , "writing on the wall" , "Sign of a future event, good or bad" .)