Most states, cities, and towns have laws, ordinances, or regulations that relate to the placement of signs on the public right of way. Generally, the law prohibits most advertising signs and billboards being placed in the public right of way, i.e. roads, highways, and streets. Any signs containing advertisements can be placed on private property outside the public right of way, but usually must be a certain distance back from the right of way. If a sign is placed illegally within the public right of way, the appropriate governmental entity governing the right of way can usually remove the sign. Even instructional street signs, such as stop signs, yield signs, etc., must go through a permit approval process, usually through the state department of transportation, in order for them to be placed on the public right of way. In most cases, acknowledgement signs, such as adopt-a-highway program signs, are also permitted on the public right of way.