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 Indiana, property owners can use 'No Trespassing' signs to deter unauthorized entry and limit liability. Indiana Code § 35-43-2-2 specifies that a person who knowingly or intentionally enters the real property of another person after being denied entry by the owner or their agent, or after being ordered to leave by the owner or their agent, commits criminal trespass, a Class A misdemeanor. The presence of 'No Trespassing' signs serves as a clear notice that entry is not permitted, which is essential for establishing the knowledge element of the trespass offense. Additionally, under Indiana's premises liability laws, property owners owe a lower duty of care to trespassers compared 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, especially if proper signage has been posted to warn against trespassing. However, property owners may still be liable for willful or wanton misconduct that causes harm to a trespasser.