Special postage for secret police (7)
I believe the answer is:
gestapo
'secret police' is the definition.
(Gestapo is an example)
'special postage' is the wordplay.
'special' indicates an anagram.
'postage' with letters rearranged gives 'GESTAPO'.
'for' acts as a link.
(Other definitions for gestapo that I've seen before include "Hitler's secret police" , "Men in black" , "Geheime Staatspolizei" , "Police detested" , "Notorious secret police" .)