Trying to enforce one's will over public property and public behavior with misleading, official-looking signs is scarcely any better than impersonating a police officer for the same effect--it's just a matter of degree.
Everything you're suggesting would be illegal, because the person would be defacing public property. There's a clear line between repainting a city owned curb or a posting a sign on a city owned streetside.
It's not -exactly- the same as painting a curb on your own property, or putting a sign on your own lawn.
Again. I agree that these Malibu owners are being crappy, but there's a difference.
The issue might not be that big in areas where nobody cares about land that much, but in NY, LA, or other big city, where the cost of land is so high, every inch counts.
So you paint the curb red and install a fake fire hydrant. Is the curb yours or not? I don't know. Can you "impersonate" a fire hydrant to stop others from parking in front of your house? Not sure. It seems like it would be illegal. Kind of like putting a fake "highway entrance" green sign on the side of your house. It is your property but if it start directing traffic into your neighbor's pool you might just get fined or sued. At least a law will quickly be created to deal with the issue.
There's definitely some funny business when it comes to signs and sidewalks; e.g., the landowner owns the sidewalk, but is required to keep it clear and level, not prohibit the public walking on it, not turn it into a flowerbed, etc.
Google says yes, in certain cases: "http://blog.lawinfo.com/2011/03/23/impersonating-a-governmen...
These fake signs try to change common practice; they are subverting the law and are quite successful at it. They are black hat hackers, in a way.
I cannot see why you would be supporting this scumbaggery.