Here's information on the Liberty Bell Token (a/k/a a Trade Check Separator), based on this listing currently for sale on eBay
Antique slot token made for the Mills Novelty Company's "Liberty Bell" slot machine, circa 1910. It is brass, round, and 21mm in diameter. The first Liberty Bell was made by Charles Fey, the inventor of the slot machine, in 1895. It was later copied by Mills, Caille Brothers and others. The subsequent Mills machine was called the Operator Bell.
The first mechanical slot machine was the Liberty Bell, invented in 1895 by car mechanic, Charles Fey (1862–1944) of San Francisco. The Liberty Bell slot machine had three spinning reels. Diamond, spade, and heart symbols were painted around each reel, plus the image of a cracked Liberty Bell. A spin resulting in three Liberty Bells in a row gave the biggest payoff, a grand total of fifty cents or ten nickels. The original Liberty Bell slot machine can still be seen be at the Liberty Belle Saloon & Restaurant in Reno, Nevada.
Charles Fey was also the inventor of the trade check separator, which was used in the Liberty Bell. The hole in the middle of the trade check allowed a detecting pin to distinguish fake nickels or slugs from real nickels. Fey rented his machines to saloons and bars based on a 50/50 split of the profits.
Here's a photo of the actual machine: