Left behind schedule after parking -- sign of a new driver (1-5)
I believe the answer is:
l-plate
'sign of a new driver' is the definition.
(learner drivers have L-plates on their cars)
'left behind schedule after parking' is the wordplay.
'left' becomes 'l' (common abbreviation).
'behind schedule' becomes 'late' (I've seen this in another clue).
'after' is a charade indicator (letters next to each other).
'parking' becomes 'p' (abbreviation on road signs).
'late' after 'p' is 'plate'.
'l'+'plate'='L-PLATE'
(Other definitions for l-plate that I've seen before include "Sign of a learner driver" , "Sign on learners car" , "A learner driver must display this" , "Learner drivers must display this" , "It denotes a learner" .)