Comment by gosub100

I thought about this too several years back before privacy erosion really got noticed. If you scanned all sn's, a db could keep track of roughly where the cash was located. if you counterfeited, you'd have to use a valid sn, clone a bunch, or pick random ones. you could have a semi-accurate signal on whether to double-check a bill if it was registered in X location but appeared in Y, and if the treasury participated, it could flag a bill immediately as counterfeit. If a criminal cloned a large number of the same sn, once one is flagged as counterfeit you could catch a _lot_ more with no effort. while it would increase friction substantially for counterfeiters, the cost would be privacy.