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I remember seeing slot cards in the Frontier back in 1985 or so. Also found the following info at the website below:

The “Slot Clubs” were born in Atlantic City in the early 1980’s when the casinos there were trying to find a way to keep players from hopping from one casino to the next. By offering a reward for their loyalty they were able to keep the player coming back. Now slot clubs are found in most major casinos. The cards are not just for slots. Most casino combine the table games and slot machines into one player’s card.

http://casinogambling.about.com/od/comps/a/slotcard.htm

Hope this helps.