atleast 6 years ago there was a thing called 'MTGox codes' where people could transfer value between mtgox, btc-e and bitstamp without touching the blockchain as the exchanges were using reserves and a code system they worked on inbetween them selves
the issue with it is people can try brute forcing the redemption codes as it was not a signature or anything s the such. people ended up snooping on people codes redeeming it and leaving the proper recipient with a 'already redeemed' message when they eventually went to try to redeem it
when it comes to redemption codes if i can reed the code on a piece of paper. i can copy it myself and the very second i hand the paper note to someone else. i can redeem the value leaving them pennyless
the only sure way is via private keys that are hidden on the face of the bank note but available by ripping a seal on the paper note.
but even then people can still make fake notes
EG make 300 notes all using the same code
paper wallets are ok for single use transactions hand to hand but not good for circulation ongoing, because the more hands a paper note passes the more chance someone in the middle is about to redeem it before the current holder
last point about the 'easy to write down codes'
if its soo easy. then it makes it soo easy for abuse
Great questions. I was not aware of the 'MTGox codes'. But I think these tickets have some unique features. In a trustless environment you can burn a ticket for a new one for each transaction (upcoming feature). You have to talk to the server but you do so anonymously. All tickets are unique. As paper money, if you lose it it's gone. If you expose all ticket codes it could be gone, but that is why these tickets have the verify code. In a trustless environment you will have to use several codes for each transaction.
In a local setup you could remove features to prevent tickets from being cashed in without going to a cashier, but this is not a feature I'm implementing in the public solution. If you lose a ticket, it's the finders keepers just like paper money.