Crossword Genius

They are for promoting a CID officer (3)

Ross

I believe the answer is:

ads

'they are for promoting' is the definition.

'a cid officer' is the wordplay.
'cid officer' becomes 'ds' (Detective Sergeant).
'a'+'ds'='ADS'

(Other definitions for ads that I've seen before include "Commercials" , "Promotions" , "Classifieds (abbr)" , "Notices" .)

I've seen this clue in The Times.
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