Old soldiers get 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' is the wordplay.
'old' becomes 'o' (abbreviation).
'soldiers' becomes 'men' (men can mean a group of soldiers).
'o'+'men'='OMEN'
'get' is the link.
(Other definitions for omen that I've seen before include "Foreshadow" , "Portent of evil" , "Warning - sign" , "premonition" , "Auspice" .)