Some laws relating to "no trespassing" signs include that they must be posted along the perimeter of the restricted area or near the area. It is illegal for an individual to post "no trespassing" signs on an area without the owner's permission. Laws governing such signs vary across states.
Alaska requires landowners to post "no trespassing" signs that are legible in English at each access point to the property. The state of New York requires that "no trespassing" signs be at least 121 square inches in size, while Alaska requires "no trespassing" signs to be at least 144 square inches in size. Most states require landowners to post "no trespassing" signs in a conspicuous manner.
The state of New York allows landowners to grant access to selected individuals using "ask permission notes," which help landowners to keep track of guests. Landowners who have granted written permission to individuals can't prosecute the same individuals for trespassing. Individuals are allowed to navigate posted waterways that are affected by tides. The public is not allowed to be on private land adjacent to navigable waterways, except for navigation purposes.
A landowner can put "no trespassing" signs on areas that are considered curtilage, or the immediate areas surrounding a house, in order to prevent government agents from accessing such areas without a warrant.