Portentous signs (5)
I believe the answer is:
omens
'portentous signs' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for omens that I've seen before include "Signs of things to come" , "Prognostications" , "Portents, prophetic signs" , "Harbingers, portents" , "Auguries" .)