Sign that independent country has upright police force (10)
I believe the answer is:
indication
'sign' is the definition.
(I know that sign can be written as indication)
'independent country has upright police force' is the wordplay.
'independent' becomes 'i'.
'country' becomes 'nation' (synonyms).
'has' indicates putting letters inside.
'upright' shows that the letters should be reversed in order (in a down clue, letters go up).
'police force' becomes 'CID' (Criminal Investigation Department).
'cid' in reverse letter order is 'dic'.
'nation' going around 'dic' is 'ndication'.
'i'+'ndication'='INDICATION'
'that' is the link.
(Other definitions for indication that I've seen before include "Sign (of something)" , "form of evidence" , "it shows" .)