Rakkikado. That's "lucky card" in Japanese. I now have two of them. I don't know what prize you would get when redeeming the lucky cards, but the offer must have expired long ago, and the two lucky cards I have were redeemed, anyway.
As for the two lucky cards, they are both on the yellow backs, and don't give any actual details on how to redeem them. I assume you'd return to the store for your prize, or at least for information on how to redeem it. Lucky cards can be found in a bunch of releases prior to BBM entering the market - most notably, old menkos and Calbees had lucky cards inserted. The prize was usually a larger card or other premium.
If you have any more information, let me know!