The famed beaches of Malibu are public; you are the owners.
However, there seems to be a concerted effort to confuse the public, to make one feel like a criminal trespasser in some exclusive enclave of millionaires and celebutants. If you aren't met by security guards at the very few public access entrances, this after navigating through barriers just to get to public parking lots, there are signs warning you that you are passing through “private property” and entering a “private beach.”
There are signs everywhere: “No Parking Any Time”, “No Stopping”, “Right to pass by permission” — the majority of which are false and illegal. It's as if the aristocracy along Central Park West and 5th Avenue has conspired to keep the public away from Central Park.
To see that the public is properly instructed on how to access the beach — your beach — the Los Angeles Urban Rangers provides an easy-to-use field guide [PDF]. From their website, you can also download a reprinted article, by Jenny Price, from LA Observed that gives you more detail.
Having both with you shouldn't necessitate carrying copies of the California Coastal Act and the state's constitution.
For those who are in Los Angeles this weekend, you can also sign up to a “safari” organized by the urban rangers, who will teach you how to navigate those invisible lines separating private-property and public lands. A “public easement potluck” is also scheduled on your beach.