Mike Caldwell, a Bitcoin enthusiast from Utah in the US, created a series of coins to serve as physical representations of Bitcoin for the purposes of entertainment, cold storage, and semi-trusted trading. Each token included a labeled denomination, which was backed by an embedded printed private key, sealed inside the coin with a security sticker to prevent idle exposure of the funds.
In late 2013, Mike Caldwell was pressured by the US government's FINCEN financial regulatory agency to cease operations, as part of its mandate to prevent unregulated money transmission. Mike complied with the cessation demand and since that time he has not produced any additional coins.
Coin variations produced included brass, silver, and gold options, with denominations ranging from a single bitcoin to a thousand bitcoins. Roger Ver and Mike Caldwell were the main vendors for the coins.
The private keys in each coin were selected and printed by Mike Caldwell, meaning that purchasers of these coins elected to trust that he made no record that would allow him to claim the embedded funds. Mike did however make a public record of addresses associated with the coins, and a public tracking website was made so that people could have some visibility into the number of coins in circulation, as well as the number of coins in which the private keys were used to deplete the embedded coin funds.