A detective impounding green trailers? (7)

I believe the answer is:
adverts
'trailers?' is the definition.
Although both the answer and definition are plural nouns, I don't see how they can define each other.
'a detective impounding green' is the wordplay.
'detective' becomes 'DS' (detective sergeant).
'impounding' is an insertion indicator.
'green' becomes 'vert' (heraldic term for green).
'ds' going around 'vert' is 'dverts'.
'a'+'dverts'='ADVERTS'
Can you help me to learn more?
(Other definitions for adverts that I've seen before include "Commercials" , "Refers or alludes to" , "Makes reference" .)
