Lightbrite – In some tissue boxes, the tissues are not attached, and you are not ripping when you take one out. In some tissue boxes, all of the tissues are attached by perforated lines, and when you pull one out you are ripping.
You can check the box before Shabbos. Simply pull up a tissue lightly. If it’s attached you will see, because it will stay partially attached if pulled lightly. Also, if it had been attached and pulled off, you should be able to see the perforations at the end.
Another way to tell – if thye are folded up, I think that means they are unattached.