Old soldiers getting a sign (4)
I believe the answer is:
omen
'a sign' is the definition.
(I know that omen is a type of sign)
'old soldiers getting' is the wordplay.
'old' becomes 'o' (abbreviation).
'soldiers' becomes 'men' (men can mean a group of soldiers).
'getting' is a charade indicator (letters next to each other).
'o'+'men'='OMEN'
(Other definitions for omen that I've seen before include "Sign of a future event, good or bad" , "Auspice" , "Portent of evil" , "Forecast" , "Prognostication" .)