Sometimes things just happen to come up. You have to follow the call of nature, you have the worst sore throat and just need a drink of water or you simply want to go outside and take a breath of fresh air. Whatever your reason, there are times when it becomes necessary to leave your slots for a few minutes. When that happens, it's always nice to know that you can come back to the machine that you were playing before you left. No matter what logic tells us about random number generators and every hand being independent, there is a superstitious place in all of our hearts that doesn't want to come back to see someone else winning on our slots. Here is how you can designate your machine.
Try the empty cup method. Put and empty coin cup on the seat upside down. This will let people know that the machine is yours and that you have simply stepped away for a few moments. This should really keep you in good shape. If you're worried about the cup falling, lean the seat against the machine. Most players know that this is also a tell-tale sign that the machine is in use, and shouldn't be played immediately.
On the other side of the issue, use manners and common sense when saving a machine. If you plan on being gone for anything longer than a quick bathroom break you can't expect your machine to stay open all night, just for you. Other people want on the machines as much as you, and it is bad etiquette to save your machine and then decide to leave for 15 minutes. If you come back to find the machine being played, you get what you deserve.