Officials work on sign (13)
I believe the answer is:
functionaries
'officials' is the definition.
(I know this)
'work on sign' is the wordplay.
'work' becomes 'function' (synonyms).
'on' means one lot of letters go next to another (in a down clue, letters appear on others).
'sign' becomes 'Aries' (star sign).
'function'+'aries'='FUNCTIONARIES'
(Other definitions for functionaries that I've seen before include "bureaucrats?" , "Officials" .)