Notices European agents (6)
I believe the answer is:
espies
'notices' is the definition.
(I've seen this in another clue)
'european agents' is the wordplay.
'european' becomes 'e' (abbreviation e.g. EU).
'agents' becomes 'spies' (secret agents).
'e'+'spies'='ESPIES'
(Other definitions for espies that I've seen before include "Spots" , "Sees (archaic)" , "Catches sight of" .)