cast iron champion spark plug bank

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I have a cast iron bank with the words "spark plug" on the right side, under the slotted screw. It is a horse, approx. 4 1/2" tall, he is sitting with his hind legs up, almost to his ears, the color is kind of dirty green, he has red around his mouth with white teeth, the coin slot is on his back. "Spark Plug" is also written on the other side. It is old, but don't know much about it -- Age and value. Can anybody tell me anything about him?