This currency is an odd ball, it exists because an activated card can exchange digits without double spending or forgery, simply encrypting using its first unique assigned, key.
It is really just the neutral default currency, and has to exist because, in pure state, the cash card does still thumb print, and thus can exchange with no app help.
What do I know about street cash?
Nothing. Haven't thought. There is nothing from stopping anyone from opening an S&L with default cash, but it cannot issue the stuff.
What is the one thing default cash can immediately do in the economy? Recognize secure device activation, and that requires a transaction. Hardware vendors of secure device should crate the secure device coin, accepted at par value as one, the prescribed value of the initial thumb print. I dunno?
Functionally,the sand box can sell milli-denominations and trade a lot of stuff. That requires a conspiracy of card holders to put part of their thumb print up as base money for a positive only bit error function, ans S&L. It would have to members only, otherwise the bots will gang up, but that is not 'no arbitrage'. But 'members only' is OK for security purposes, sandbox security does not obey no arbitrage. The thumb print coin is universally available per secure element, untradeable, and ship them around for security purposes.