No trespassing sign protect you from injury suits>

This is not a criminal defense question. You are seeking advise on a civil law matter. I will change the practice area for you from "criminal defense" to "lawsuits and disputes" and in that way I hope that I will have been helpful.

It has all the protection of an umbrella during a nuclear attack. You cannot put up a sign that waives liability. Furthermore, the law holds your driveway and other portions of your front curtilage exist so the public can approach your door to engage in congress with you. Put up a fence and lock it if you can; otherwise, a sign stating "Watch Your Step" might help mitigate any damages or it could attract people who purposely fall.

Such a sign will not prevent people from suing you and prevailing if you are otherwise negligent. You can certainly argue in such a case that the person should have known that they were not welcome there, but it is not an absolute protection.