oo those are pretty cool! i'd say it hurts a good amount. it's pretty much directly on your bone.. there's only thin skin on that area of your body. of course everyone is different when it comes to pain but i'd say you'd definitely feel it and it would hurt a bit.
Everyone handles pain differently, but still, places where the skin is thin and/or close to the bone are going to hurt the most. I got my tattoo on my shoulder blades and it was pretty rough... I can't image getting one done along my spine.