Sign is a bit gruesome (4)
I believe the answer is:
omen
'sign' is the definition.
(omen is a kind of sign)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for omen that I've seen before include "Forecast" , "Augury, portent" , "Foreboding" , "Auspice" , "Sign of likely future event" .)