Young guy to cover vehicle after parking notice (7)
I believe the answer is:
placard
'notice' is the definition.
(synonyms)
'young guy to cover vehicle after parking' is the wordplay.
'young guy' becomes 'lad' (I've seen this in another clue).
'to cover' indicates putting letters inside.
'vehicle' becomes 'car' (car is a kind of vehicle).
'after' is a charade indicator (letters next to each other).
'parking' becomes 'p' (abbreviation on road signs).
'lad' going around 'car' is 'lacard'.
'lacard' after 'p' is 'PLACARD'.
(Other definitions for placard that I've seen before include "Make card, pal, into kind of ad" , "Notice carried for public display" , "Sign for public display" , "One taken on march" , "Poster" .)