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 South Carolina, property owners can use 'no trespassing' signs to deter unauthorized entry and limit liability. Under South Carolina law, specifically S.C. Code Ann. § 16-11-600, it is illegal for a person to enter another's property without permission after having been warned not to do so by the property owner or by notice posted on the property. The signs must be conspicuous and placed at each road entrance and the boundaries of the property. The presence of these signs serves as a warning that entry onto the property is not allowed without the owner's consent, and it establishes that any person entering the property without permission is trespassing, which can lead to both civil and criminal consequences. Additionally, South Carolina follows the common law tradition where a lower duty of care is owed to trespassers compared to invitees or licensees. Therefore, posting 'no trespassing' signs may also help landowners reduce their liability in the event a trespasser is injured on their property, as it demonstrates that the trespasser was not invited and that the owner took reasonable steps to warn against trespassing.