Somebody please post the rules. I don't think I was around when this started. I have been curious, too.
Here's a couple of Bingo Cards.
OK, ipad won't let me link, but if you do a search for Bingo Cards, the thread on Etiquette will come up with some cards.
Yeah, I liked hers because Maggie and I are squares on those cards, but I can't find it!