Does a "No Trespassing" sign protect a homeowner in Missouri?

I don't know MO law specifically, but if it is similar to the law in the jurisdictions in which I practice, there is no way to completely immunize yourself from liability, but the "no trespassing" sign might help (although I wonder whether any reasonable person old enough to read the sign would think that they had permission to trespass if there was no sign.)  If someone gets hurt on your property, the question will be whether you were negligent, and whether your negligence caused the damages.  For example, if you have a swing set on your property, and a child should trespass on your property and have an accident on the swing set, your liability will depend on whether such an accident was forseeable (it seems to me forseeable that a child might be drawn to a swing set, and that a "no trespassing" sign is insufficient to ensure that doesn't happen), and whether you took reasonable steps to prevent it from occurring (for example, having a fence around the yard, etc.)  A "no trespassing" sign would not, in my opinion, help you much in such a context.  If, however, the accident occurred when an adult Jehovah's Witness slipped on your walk, which was cracked and uneven, a jury might think that the sign was all the precaution needed.  The standard is reasonableness, which is not subject to a bright line test, particularly when predicting what might occur in the future, although sometimes there are statutory gudielines (for example, the town code may provide that you can't have a pool unless you have a six foot high fence surrounding it, or can't have a swing set unless you have a mat or similar soft surface underneath.)