Posh car takes meandering course under parking sign (9)
I believe the answer is:
precursor
'sign' is the definition.
(precursor is a kind of sign)
'posh car takes meandering course under parking' is the wordplay.
'posh car' becomes 'rr' (I've seen this in other clues).
'takes' is an insertion indicator.
'meandering' indicates an anagram.
'under' is a charade indicator (letters next to each other).
'parking' becomes 'p' (abbreviation on road signs).
'course' is an anagram of 'ecurso'.
'rr' enclosing 'ecurso' is 'recursor'.
'recursor' after 'p' is 'PRECURSOR'.
(Other definitions for precursor that I've seen before include "harbinger of what is to follow" , "Man coming before me" , "Herald" , "One coming before" , "Forerunner, predecessor" .)