Under Australian Law, all land is originally communal land. The federal government owns many acres of land and some might think that a wilderness area may be public property. They might fish, camp or hunt on private property by accident. A Keep Out or No Trespassing sign can control access to land by identifying it as private property. It is a good reminder to children also. Under the law, an individual who sees a No Trespassing sign cannot enter, remain or participate in any activity on property with this written notice. Legally, anyone must ask your permission to be on your land, but you may not be there to discuss this issue with them 24/7/365. A No Trespassing sign and fence will send the message that no one can be on your private property without authorization. The Penal Code requires that land owners post conspicuous signs near the primary entry points of the area to be closed to the public. "Can I Trespass on Land With No Posted Signs?" The law tries to keep a balance between the rights of regular people to enjoy land and the rights of land owners. If there is no fence, the land has not been improved, looks unoccupied and has no posted sign, then someone can assume the land is public for the use of anyone. Under the natural squatter law, land should be used by the community for productive purposes. Unused land returns to communal ownership. Trespassing is officially illegal on unposted property that has been improved, used and fenced in. If a land owner or occupant requests a trespasser to leave verbally or with a written letter, the trespasser must leave. Generally, the Keep Out sign is basically the same as the No Trespassing sign. The land owner, legal occupant or an authorized representative can post the No Trespassing or Keep Out sign on any portion of the land and identify any activity that is prohibited. Even if you post a No Trespassing sign, you can grant permission to designated individuals. That is your right as a property owner. Trespassing laws vary by state.