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 Oklahoma, property owners can use 'no trespassing' signs to deter unauthorized entry and reduce liability. Oklahoma law recognizes the importance of such signs to establish that individuals entering the property without permission are aware they are trespassing. Under Oklahoma statutes, specifically Title 21, Section 1835, a person who willfully enters the land of another after being forbidden or without permission may be guilty of trespassing, which can carry both civil and criminal penalties. The presence of 'no trespassing' signs helps to establish that the trespasser had clear notice that entry was not allowed. Regarding liability, Oklahoma follows the general rule that landowners owe a lower duty of care to trespassers than to invitees or licensees. If a trespasser is injured on the property, the fact that they ignored 'no trespassing' signs can be used to argue that the property owner should not be held liable for those injuries, as the trespasser was on the property without consent and had been warned against entering.