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 Louisiana, no trespassing signs serve as a clear indication that entry onto the property without permission is prohibited. According to Louisiana state statutes, particularly RS 14:63, criminal trespass is defined as the entry of any person onto property without express, legal, or implied authorization. The presence of no trespassing signs can help establish that individuals entering the property are doing so without permission, which is necessary for criminal liability to attach. Furthermore, under Louisiana law, property owners generally owe a lower duty of care to trespassers than to invitees or licensees. This means that if a trespasser is injured on the property, the owner may have a stronger defense against liability claims if they can show that they took reasonable steps to warn against trespassing, such as posting no trespassing signs. However, it is important to note that even with no trespassing signs, property owners may still be liable for willful or wanton misconduct or for injuries caused by activities considered attractive nuisances to children.