I don't really think this is a great idea because the assumption here is that people want to recycle but just forget to do so or are not motivated enough. It's simplifying matters by stating that an attractive sticker will courage one who does not recycle to to do so if he/she sees the sticker in time. I believe we do not recycle because it seems inconvenient. We would rather throw the item in the first bin that comes our way rather than go out of our way to a recycle bin. Just my 2 cents!
I believe recycling is still a big issue since a solution which is convenient to the user has not come up till now. For instance, your solution would be much better if instead of the user, the in charge of the recycle bin can use a scanner to determine which item goes into which recycle bin rather than making it more inconvenient for the user.
I think the bag should be available at leading stores rather than me having to take it along when I go shopping but having said that, it brings together a great social initiative which is "#cool" at the same time.