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 Hampshire, property owners can use 'no trespassing' signs to deter unauthorized entry and reduce liability. Under New Hampshire law, RSA 635:2 defines criminal trespass and indicates that a person is guilty of a misdemeanor if, knowing that they are not licensed or privileged to do so, they enter or remain in any place. Posting 'no trespassing' signs clearly communicates that individuals are not permitted to enter the property without authorization, which can establish the knowledge requirement for criminal trespass. Furthermore, New Hampshire follows the traditional common law approach to trespassers, which means that property owners owe a lower duty of care to trespassers than to invitees or licensees. By posting 'no trespassing' signs, property owners may limit their liability if a trespasser is injured on their property, as the signs can serve as evidence that the trespasser was warned about the risks of entering the property.