First, let's be clear that this is not a Polish tradition. But this traditional German ornament and the story behind it is popular among many Polish families who either lived in or near German territories.
Each 3" ornament is boxed and comes with the traditional story. Here it is:
The pickle ornament was considered a very special tree decoration by many families in Germany. There the fir tree was traditionally decorated on Christmas Eve. For good luck, the pickle always was the last ornament to be hung on the tree with mother and father hiding it in the green boughs among the other ornaments. When the children were allowed to view the splendor of the decorated tree on Christmas morning they would gleefully begin searching for the pickle ornament. They knew that whoever found that special ornament first, would receive an extra little gift left by St. Nicholas for the most eager child.