In Tesco near me (in the UK) they have only the 'Zero' version of Monster which carries the promo codes and Ghosts decals on the can.
I'm sure more will roll out shortly.
Also the code is under ring pull, it's a little hard to read to be honest.
On the can it clearly says "Promotional ring pulls available from 31.10.2013 to 31.03.2014. Register the code found under the ring-pull online by 31.03.2014" So my best guess would be that we can't register the codes for another 12-24hrs from the time of this post.