There's an app called "Our Malibu Beaches" with all the relevant info

It's not particularly pleasant to get to some of them, and occasionally requires going at low tide. It's a rocky area, with some natural rock outcrops that go all the way to the water, and some of the folks have built out fences and rock walls and such in a manner that means you're likely to get wet getting through if it's high tide. I happen to enjoy that kind of strenuous hiking/exploring, so it wasn't really lacking in fun for me, but I doubt people just wanting a day at the beach would consider it reasonable. It might even be dangerous in some cases.

I haven't been to Malibu in a few years so mapping is not an option; I'd need to walk/bike around again to know where the "private" beaches are. But, pretty much if you walk in either direction on the beaches in Malibu, you'll find examples of it...some are more difficult than others.

I feel particularly strongly about protecting the commons, like parks and beaches and waterways, and Malibu rubbed me all kinds of wrong ways, in being such a "playground of the rich" while excluding everyone else. Despite it being illegal, the entire local government seems complicit in the heist of public resources.

Someone created an app to show such areas and access routes. Can't search for it myself just now...

Lol. Not just fake signs. There are also Locked doors. Security guards.

All illegal.