Just a warranty label. Pretty common that certain shops used these type of labels to be honest.
It says: 3 Month guaranty. Thanks for buying.
Don't store the game in a too hot/cold place, don't throw it, don't open it etc
Don't put water to it, avoid dirt etc etc.
If you have a claim, contact the shop where you bought it.
Famikon-shop-chain Takarajima (Takarajima).
+ address.
Nothing special, just a warranty sticker

This chain was based in Niigata just for curiosity.