No trespassing signs should be conspicuously installed at private property approaches, entrances, and any places where they cannot be ignored. Your requirement will depend on your property size and the number of ways and approaches visitors may use to enter. Your state may also require you to post a certain number of no trespassing signs depending on the size of your property. For example Nevada Law NRS 207.200 requires no trespassing signs to be placed in direct line of sight and at intervals no more than 500 feet apart.