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 Alaska, property owners can use 'no trespassing' signs to deter unauthorized entry and reduce liability. Alaska Statutes Section 11.46.330 defines criminal trespass and indicates that entering or remaining on property with notice against trespassing is illegal. Notice can be given through personal communication, posted signs, or fencing. The signs must be conspicuous and designed to reasonably communicate the prohibition of entry. If a person enters or remains on the property without permission after notice has been given, they may be subject to criminal charges. Additionally, under Alaska's premises liability laws, landowners owe a lower duty of care to trespassers than to invitees or licensees. Posting 'no trespassing' signs may help landowners demonstrate that they took reasonable steps to warn against entry, potentially strengthening their defense against liability claims should a trespasser get injured on their property.