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 Dakota, the use of 'no trespassing' signs is recognized as a method for property owners to communicate that entry onto their land without permission is not allowed. According to South Dakota Codified Laws (SDCL), particularly SDCL 22-35-6, entering or remaining on someone else's property after noticing such signs can constitute criminal trespass, which may be punishable by law. The presence of 'no trespassing' signs can serve as the required notice that entry is prohibited, which is necessary for establishing civil or criminal liability for trespass. Furthermore, under South Dakota's premises liability laws, property owners owe a lower duty of care to trespassers compared to invitees or licensees. Therefore, posting 'no trespassing' signs not only helps deter unauthorized entry but also potentially reduces the landowner's liability if a trespasser is injured on the property, as it clearly establishes that the individual has entered the property without permission.