I'm going to start leaving notes on people's cars.
How did it come to this? In what way do you think leaving notes would be good?
People are parking on my private property. Writing notes will threaten them not to do that again.
It's understandable that you're upset that people are parking on your property without your permission. However, threatening them by leaving notes on their cars is not appropriate behavior. Next time someone parks on your property without your permission, contact the authorities so that their car can be towed away.
I never thought of that. This is better than leaving notes now. I could put a sign there first though. What do you think?
A sign would be fine, anything but leaving notes that threaten. At least with either of the two we mentioned they would have a better understanding.