On Mon, 25 Jul 2016 05:02:19 -0000 (UTC), Henry Jones wrote:

A suggested legally accepted text is:
PRIVATE PROPERTY
TRESPASSING/LOITERING FORBIDDEN BY LAW
VIOLATORS WILL BE PROSECUTED
CALIFORNIA PENAL CODE 602

Here's another California cite:
http://police.escondido.org/sign-requirements.aspx

Per PC 553 repeats that the required keywords a
"Trespassing-loitering forbidden by law

It seems also that "Private Road, No Trespassing" can also be used.