Fix every second of six 'Nigeria' signs (7)
I believe the answer is:
ingrain
'fix' is the definition.
(thesaurus)
'every second of six nigeria signs' is the wordplay.
'every second of' indicates alternate letters.
'six'+'nigeria'+'signs'='sixnigeriasigns'
The alternate letters of 'sixnigeriasigns' are 'INGRAIN'.
(Other definitions for ingrain that I've seen before include "Raining? (anagram)" , "Impress deeply on the mind" , "Fix" , "deeply impressed" , "Firmly establish (habit)" .)