No longer parking is allowed, that's clear (8)
I believe the answer is:
explicit
'clear' is the definition.
(I've seen this before)
'no longer parking is allowed' is the wordplay.
'no longer' becomes 'ex' (prefix meaning former or onetime).
'parking' becomes 'p' (abbreviation on road signs).
'is allowed' becomes 'licit' (I've seen this in other clues).
'ex'+'p'+'licit'='EXPLICIT'
'that's' is the link.
(Other definitions for explicit that I've seen before include "Spelled out" , "leaves nothing to the imagination" , "Hard-core" , "Stated without concealment" , "Unambiguous" .)