I just got off the phone with trarric dept.(AKA Transport Dept. San Pedro)
They say 'yes' against the law for motorized vehicles on beach and 'Yes' Segway two wheeled things are same difference , They advise a written report to the Town Council to report violation and then they can act on written report.
I belive a Sign on the beach is a good Idea but a nice friendly sign so It isn't read as 'unfriendly area' to the people walking the beach.