The next update for BBM is right around the corner (as in days away). It will bring along some new features including sponsored BBM Channels content as well as BBM Stickers. If you just can't hold out for the official update to arrive though, a leaked version is available now that gives you plenty of sticker-loving fun.
You'll have to sideload the leaked version on your device to use it. It appears that things are running smoothly for the most part, the exception being that paid stickers aren't available for purchase.
Standard rules apply to this one too - it's unofficial hence not supported, so use at your own risk. If anything breaks it's all on you.