Put out a live cat trap, trap the cats and take to humane society. The owners will need to pay boarding fees, plus all updated vaccines, and a fine to get the cat back. After several cats or several fines they will get the idea.
I would have gone this route before the police but that is me.
I do understand your anger, that cat pee will never be out of your seats as the uric acid will soak into the foam pad, just wait for a hot humid day, you will smell it !!!!
Now that is a classic idea...never thought of that one. Only problem is she is the type that wouldn't go get the cats. She does some sort of cat rescue for the humane society and now she is doing some kind of dog rescue as well. So far, we have had a few hot days and I haven't noticed the smell, but if I do, then unfortunately for them, they will be buying me a new seat.