Okami Haundo
Member
There is nothing in the game boxes except for the game card, but you can link your physical game to your My Nintendo account via the game's options (-/+ on the main screen when selecting the game > My Nintendo Rewards Program (or something like that, I'm translating from French)).
Thanks for this! Honestly, that's a really smart approach. Club Nintendo was a little too easy to exploit by having physical codes. I had a friend who worked at Gamestop and used to pull them out of used copies all the time.