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 Virginia, property owners can use 'No Trespassing' signs to deter unauthorized entry and limit liability. Under Virginia Code § 18.2-119, it is illegal for any person to enter or remain upon the lands or premises of another after having been forbidden to do so, either orally or by posted signs. The signs must be clearly visible and posted at all entrances to the property. If a person enters the property without permission after such notice, they may be subject to criminal trespass charges. Regarding civil liability, Virginia follows the common law tradition where landowners owe a lower duty of care to trespassers than to invitees or licensees. By posting 'No Trespassing' signs, landowners make it clear that individuals are not welcome, which can reduce the landowner's liability if a trespasser is injured on the property. However, Virginia does recognize the 'attractive nuisance' doctrine, which could impose liability on landowners in certain situations where children are enticed onto the property by an attractive hazard and are injured as a result.