Sign left on hospital department (7)
I believe the answer is:
portent
'sign' is the definition.
(portent is a kind of sign)
'left on hospital department' is the wordplay.
'left' becomes 'port' (left side of a ship - opposite of starboard).
'on' says to put letters next to each other.
'hospital department' becomes 'ent'.
'port'+'ent'='PORTENT'
(Other definitions for portent that I've seen before include "Foreboding" , "Augury" , "Sign, omen" , "Warning of momentous event" , "bad sign" .)