I was thinking that on the back you could have the coin number, the "faucet" code, and the amount of GRC the code is worth.

Or to make it easier you could combine the coin number with the faucet code. So if you manufacture 100 coins and give them out, the code could show the coin manufacturing number followed by 6 randomized characters. So the codes would go 001XXXXXX, 002XXXXXX, 003XXXXXX, ... 100XXXXXX. Where the X's are the randomized characters. This way we could have each coin have the same value, or different values, without the risk of people stealing others rewards. Hell you could even make it like a lottery, where some of the coins have 1000 GRC, while others have 10. What do you think?