This is a consecutive bidding game where players "bet" the total # of occurences of digits on all bills involved in the hand. The winner of each hand is decided when players call somebody's bid. If the person makes the bid he wins everybody's dollar, if he loses the bid he pays everybody a dollar.
It's frequently played in bars, where the ones can usually be recycled with bills in the cash register, which eliminates any chance of memorizing/recognizing bills.
You have to call a higher hand than the last guy that called, so eventually if you can't beat what he called you have to lie, if you think he lied, you call bullshit on him.