The rental company can bill you for it. In my few experiences in Europe, it never actually happened. In France I know I triggered a camera, but never received anything. In Germany I got a letter form Avis saying I had been caught speeding on the Autobahn, and I'd be getting the ticket. But it never showed up and I didn't get billed. I'm pretty sure I got one for driving in the no vehicle area of Granada but never heard back on that one either. I tihnk they may look at the cost of dealing with it, and if it isn't worth their time they choose to write it off. I'd imagine a parking lot ticket pretty much gets ignored by rental companies. Just a guess though.
And ya, I know I sound like a scofflaw, but all 3 were due to "don't blame me, I'm just a tourist!" I now know that this sign does not mean "bear claws ahead".
