Originally Posted by
exerda
It *is* placed inside the last page. I've never heard of them putting it on the back cover where the various security staff put stickers, where airlines stick things, etc.
I found this picture online:
I suspect that most interviewers placed the sticker inside, but some have decided to affix it to the back. The one benefit to having it on the back is that it is easier to flash to a CBP officer in a booth. Opening and holding up a passport with the sticker inside is marginally more difficult.