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 Maryland, property owners can use 'No Trespassing' signs to deter unauthorized entry and limit liability. Maryland law recognizes that posting such signs is a way to provide notice that entry onto the property without permission is not allowed. Under Maryland Criminal Law Section 6-402, a person may not willfully enter the property of another without lawful authority and after being notified by a posted sign against trespassing. If someone enters the property without permission, they may be subject to criminal penalties. Additionally, Maryland follows the common law tradition where landowners owe a lower duty of care to trespassers than to invitees or licensees. By posting 'No Trespassing' signs, landowners make it clear that individuals are not invited onto the property, which can reduce the landowner's liability if a trespasser is injured. However, landowners may still be liable for willful or wanton misconduct that causes injury to a trespasser.