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 Delaware, property owners can use 'No Trespassing' signs to deter unauthorized entry and limit liability. Delaware law recognizes the importance of such signs in establishing that individuals entering the property without permission are aware they are trespassing. Under Delaware Code Title 11, §§ 820 and 821, trespassing is a criminal offense, and the presence of clearly posted 'No Trespassing' signs can serve as evidence that the trespasser had notice that entry was not allowed. This can lead to civil and criminal liability for the trespasser. Furthermore, Delaware follows the common law tradition where a landowner owes a lower duty of care to trespassers compared to invitees or licensees. By posting 'No Trespassing' signs, a landowner may strengthen their defense against liability claims should a trespasser get injured on their property, as it helps demonstrate that the trespasser entered the property without permission and was thus owed a minimal duty of care.