Well I learned today that even cash is not as anonymous as I (and I presume most of us) thought it was.  Apparently the latest "anti-terrorism" intrusion is that the serial numbers on currency are being tracked - not 100%, but if you receive or deposit cash in an ATM - the serial numbers are scanned/recorded and can be traced and tied to your specific transaction.  Likewise, Most banks now track and record the serial numbers for currency they receive and return each day, so even if you do transactions in person, while the specific serial numbers may not be directly tied to you, authorities can review the video and other records that most all banks now keep and determine who made deposits/withdrawals that day.  They track cash down to the specific teller who receives/disburses it, so you can be narrowed down to one of a few people very easily.  Looks like the ultra safe course of action is to use currency you receive as change in a cash purchase transaction. Of course this is aimed at tracking terrorist (at least for now).