This is what Mike Poole posted about them on the slot card bbs:

"It's like a cash card, you charge it up and then you can move from machine to machine with your 'bankroll' on the card. When the card is empty, charge it back up or throw it away. Occasionally, you find one with a few dollars credit left on them.

They are used all across the country. I put quite a few of these cards in 'circulation' (giving away or trading them) from the Alabama-Coushatta reservation casino in Livingston Texas. There are NONE that I know of in the Lake Charles Lousiana Casinos or In the Alabama-Coushatta in Kinder La. Others will have to report on their areas.

Maybe this will shed a little more light on these cards."

and here is a link to there website
http://www.cadillacjack.com/