Sample stickers will usually be stuck on top of the bar code, as you can see in this image. There will typically be one on both the obi and on the back liner. The text on the sticker might differ from case to case but it tends to be the same size. It won't be easy to remove it without ruining the paper it's attached to.
"SAMPLE" will also be branded on the inner rim of the disc, as you can see in this image.
