Are you saying that before you spend it there thing a need ? Confirmation ? Am i right ? What key ate you talking for ? I dont understand
Bitcoin works with digital signatures. They are similar to real signatures, but you need certain data to create the signature, the private key. Everyone that knows the private key can spend the bitcoin that are associated with it. If you want to have a bill for bitcoin, my understanding is that you would need the private key on that bill (e.g. under a sticker so not anyone can see it). When you (or the country issuing it) create the bill you have the private key somewhere else. Now if you give me the bill its only useful as a paper bill if you can convince me that you have destroyed all other copies of the private key. Otherwise you could go home use the private key and scam me. Since I see no way for you to convince me, I would use the private key on the paper bill and transfer the bitcoin to a private key I know is mine and only mine. After I have done that the bill is worthless.