[US: CA] Is it illegal to put stickers/magnets on other people's cars

I live in a major city and tons of people park in my driveway all the time. Unfortunately, by the time the city/tow people come, they are long gone. They typically block my driveway for 5-10 minutes (multiple people each day).

Is it illegal for me to put a sticker or magnet on their car? I don't want to make their life difficult- they wouldn't be hard to remove stickers or anything, but I want to put something there. If not, then my other option is to leave a note on every car.

Thanks for advice!

Location: California, US

Author: Enough_Rooster6212