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 Florida, the use of 'no trespassing' signs is recognized as a legitimate way for property owners to warn individuals against unauthorized entry onto their land. Under Florida Statute § 810.09, a person who willfully enters or remains in any property without being authorized, licensed, or invited, and who is warned by the owner or lessee of the property or by a person authorized by the owner or lessee to not trespass, is committing the offense of trespassing. The presence of 'no trespassing' signs serves as a clear warning and can establish that an individual has knowledge that they are not permitted to enter the property. This can lead to civil and criminal liability for trespassing. Additionally, Florida law generally provides a lower duty of care to trespassers than to invitees or licensees. Therefore, posting 'no trespassing' signs may also help to limit a property owner's liability in the event that a trespasser is injured on the property, as it demonstrates that the trespasser entered the property without permission and was adequately warned of the private nature of the property.