Hello Doves,
 
Let me just say that it is entirely possible to create the "Mark" today, in this day and age.  It does go beyond verichip's implantable chip.  I believe the "Mark" is an entire system that is now coming into form.  First we have an ID system that "marks" or "tags" us, similar to our Social Security Numbers here in the USA. These ID numbers would then exist on an extremely large and fast database.
 
1.  How global can the "Mark" be?
Windows Server and Microsoft's Database just won't cut it for this type of need.  Instead it will most likely be a Linux based cluster, probably running the Oracle Grid, in a world wide distribution.  Today we have the Akamai network, the largest linux cluster in the world.  The Akamai network has "nodes" dispursed around the globe to speedily and securily hand out most mainstream websites.  There is the blueprint for the "Mark" database, and it is already working and effective.  Broadband getting cheaper here in the states and becoming more accessible to the rest of the world (including poor third world countries) and the tech community trying to make extremely cheap laptops ($100) for those third world countries making it even more available.
 
2.  Stores and Commerce
The development of the internet and the increasing availability of broadband will make it relatively easy for stores, banks, and other commerce type businesses to switch to the "Mark" based economy.  With a global database that has all of our assigned Credit Cards and Bank Accounts tied into it, the main upgrade would be to the Point of Sale systems and their swipe systems.  If that is even necessary.  The "Mark" based economy supposedly would allow you to load up your cart, and then walk out the door.  The RFID tags in the cart will tell the system to add it up and the Chip will deduct it from one of your available accounts.  Folks, the RFID system is already operational and making its way into the stores and warehouses of Wal-Mart.  They just need to tune it for ringing up your bill and collecting payment.
 
3. Renewable powersource for the "Mark"
About two years ago, a german company developed a method for tapping into the electricty that exists inside the human body.  It isn't a lot of electricity, but enough to power an implanted chip.