Seeing I have no road right in front of me, I am not qualified to respond.
However, I think I would appreciate someone approaching me to ask, even though I have no legal grounds if properly parked. If I had any suspicions about theft or fly-dumping, then yes, I would approach the appropriate authorities. I did this once in the US when I had some jerk park in one of my slots (using both of them) in a block of apartments and I had the car removed; that was of course on private ground and a different legal jurisdiction.