It’s amazing how with just one letter dropped, the meaning of this sentence changes completely. What they meant to say is that illegally parked cars will not be fine, as they will get a ticket, or worse, and they accidentally said the exact opposite – illegally parked cars will be fine, absolutely fine. Feel free to park.
It should be clear to anyone seeing this sign that they meant to say “fined,” and someone messed up the one simple task they had; but if you really wanted, you could insist on your innocence and claim you were just following the orders of the sign, and you honestly believed it would be fine. The sign will be on your side.