Property line argument.

[onrway]

Not that you will, but you could end up in court. If you did, then you would want to show that you had served proper notice. I would talk first, play dumb. Ask questions and then nicely ask them to move the vehicles. Write down the date and the jest of the conversation. Give it a reasonable time say 30 days. If nothing happens then follow up with a registered letter. Go from there.

[DTisme]

I'd go to the neighbor and ask if they know who owns the cars. It's a good way to open the conversation without being accusatory. Like Royall says, they might not even be theirs. If they're NOT theirs, there's supposed to be some county program to pull abandoned cars out of the jungle. Not sure if it's still in force and not sure what the deal is when they're on your own property.