Postage for secret police (7)

I believe the answer is:

gestapo

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'secret police' is the definition.
(Nazi secret police)

'postage' is the wordplay.
'postage' can be anagrammed to 'GESTAPO'.
However, I am not clear how the anagram is indicated.

'for' acts as a link.

Can you help me to learn more?

(Other definitions for gestapo that I've seen before include "Brutal force" , "Police detested" , "Hitler's secret police" , "State police in Nazi Germany" , "war force" .)

I've seen this clue in The Irish Independent.

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