Unspoken seat understanding

Whether you are at a movie, a concert, play, or some sort of show you will always see reserved seats. Some seats are actually reserved for certain people with signs that say reserved....but for the not so truly reserved seats, individuals choose the reservation method of placing an item on the seat. We don't have to ask people that have placed a sweater or program guide on the seats next to them whether the seats are available, because this act in itself shows others that they have people coming to sit in those seats and some point in the future.