Notice in park or rehab centre? (4,3,3,5)
I believe the answer is:
keep off the grass
If this is the answer I cannot explain how the clue works.
Can you help me to learn more?
(Other definitions for keep off the grass that I've seen before include "No drugs" , "DD Don't Smoke Cannabis" , "Sign on lawn" , "Don't reach the green" , "sign - one seen in park?" .)