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 Mexico, property owners can use 'no trespassing' signs to deter unauthorized entry and reduce liability. According to New Mexico Statutes Annotated (NMSA) 30-14-1, criminal trespass involves knowingly entering or remaining on private property without permission. The presence of 'no trespassing' signs serves as clear notice that entry is not allowed, which is necessary for establishing criminal trespass. If a person enters the property without permission after such notice, they may be subject to criminal penalties. Additionally, under New Mexico law, property owners owe a lower duty of care to trespassers compared to invitees or licensees. This means that if a trespasser is injured on the property, the owner may have a stronger defense against liability claims, especially if the trespasser ignored posted 'no trespassing' signs. However, this does not absolve property owners of all responsibility; they cannot willfully or wantonly cause injury to trespassers.