I believe that you are referring to the fact that if you put a sticker or a piece of tape on an inflated balloon, you can poke a needle in that spot (the tape or sticker) and the balloon won't pop. The reason for that is simply that you have reinforced the skin of the balloon at that very point. When you inflate a balloon, its "skin" is under a lot of tension and that is why poking it with a needle leads to it ripping completely. As you will know, it won't do the same thing when you poke a deflated balloon with a needle. The tape or sticker now holds on to a larger part of the balloons surface. So it can take over sustaining the pull from the tensioned skin around the sticker when the skin below it gets punctured. The pull it experiences is not strong enough to rip the sticker. But (on a side note) if you had a balloon with very high pressure inside (made from thick rubber), a sticker that you put on there and poke through might just get ripped as well!

That is a pretty neat trick isn't it?

When you stick a pin in a balloon without the sticker it pops because the tip of the pin is stretching the rubber until it breaks. If you place a piece of tape or a sticker on a balloon it reinforces the rubber and does not allow it to stretch to the breaking point when the pin pierces the balloon.