I'd say fake the twelve bars are worth a cool million at spot, especially for static prop to much hassles with security to have it onsite
Do they look like copies of real bars (maybe bought from Alibaba :lol or is even the design made up for the movie?
Looks like something out of Air Force One- http://www.ebay.com/itm/3-PRESIDENTIAL-SEAL-TREASURY-GOLD-BAR-REPLICAS-PROP-/252384462741
They are double fakes. 1st obviously they don't use real gold and make them up, note all the serial numbers are the same, they have used the same mould/stamp on all of them. 2nd they haven't modelled them on any real bars - looks like US eagle seal and USA1234 serial number on a kilobar, none of that corresponds to any real bar, they just went with what looks good - most refiner stamps are boring.