vault unless needed. The Bellagio Motorcycle Bandit suddenly appears and grabs handfuls (hands full?) of high value chips off a table and runs out of the casino laughing maniacally; jumps on his bike and peels away. The guards prefer not to shoot him for fear of hitting other patrons or the slot machines. The casino immediately halts all card games for a moment, brings out the backup chip set and takes back those high-value chips still at the tables and in players' hands. Then they scan those chips to determine the serial numbers of the stolen chips. Meanwhile the games go on with the replacement chips. Now, if the Bellagio Bandit re-appears (in street clothes) with some high-value chips to "redeem," the casino knows those are some of the stolen items and can jump on the crook and pound him into submission. It happened once. At the Bellagio, natch!

The better question would be, how do any of the "secret" backup chip set make their way out of the vault and into collector hands?