The chip is from the Major Riddle era. Major Riddle owned a percentage of the Dunes and also liked the "Silver" title; Silver Nugget, Silver City and Silver Bird. He also built the Holiday International Casino, which eventually became the Park before it changed to Main Street Station.

The Silver City was sold off to Circus Circus Enterprises and these cards are from the Circus Circus Era... If anyone has an example of cards during the Major Riddle era I would love to see them. My guess is that generics were used.