No trespassing signs can be useful to property owners—especially on large tracts of land or land that is not developed—to put persons entering the property on notice that the property is private property and if they do not have permission to enter, they may be committing civil and criminal offenses related to trespassing. In some states notice is required for a trespasser to have civil or criminal liability for entering the property without permission.

No trespassing signs may also protect a landowner against liability to a trespasser, as a lower duty of care is owed to trespassers in some states, and putting a person entering the property on notice that they are trespassing may strengthen the property owner’s defense against any liability claims if the trespasser is injured on the property.

In New Jersey, property owners can use 'No Trespassing' signs to deter unauthorized entry and limit liability. Under New Jersey law, specifically N.J.S.A. 2C:18-3, criminal trespass occurs when a person enters or remains in a place where they are not licensed or privileged to do so, especially after notice against trespass is given by communication, posting, or fencing. Posting 'No Trespassing' signs clearly and conspicuously can serve as such notice, making it easier to prove that a person has committed trespassing if they ignore the signs. Regarding liability, New Jersey follows the traditional common law categories of entrants to land: invitees, licensees, and trespassers, with the lowest duty of care owed to trespassers. If a property owner has posted 'No Trespassing' signs, it may help demonstrate that they have fulfilled their limited duty to trespassers, potentially reducing their liability if a trespasser is injured on the property. However, the owner may still be liable for willful or wanton injury to trespassers.