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 Ohio, property owners can use 'no trespassing' signs to deter unauthorized entry and reduce liability. Ohio Revised Code Section 2911.21 specifies that a person without privilege to do so is prohibited from entering or remaining on a property if notice against unauthorized access is given by actual communication, posting of signs, or fencing or other enclosure. The presence of 'no trespassing' signs serves as a clear indication that entry is not permitted, which can establish the basis for criminal trespass charges against violators. Furthermore, under Ohio's premises liability laws, property owners owe a lower duty of care to trespassers compared to invitees or licensees. By posting 'no trespassing' signs, landowners may strengthen their defense against liability claims should a trespasser sustain injuries on their property, as the signs demonstrate that the trespasser was not authorized to be there and was warned of the private nature of the property.