I would assume it's a tag that was attached to one of the company's products. They sold related items such as polishes as well as shoes.
This, from a Mount Carmel [Pennsylvania] newspaper dated 7th April, 1915
The 20th Century Shoe Company now located at 10 North Oak street, will move to the corner of Oak and Fourth streets on or about April 10th and will continue to give the same GREAT VALUES they have been giving the past four years.
The store is being remodeled to give you the best and most efficient service possible, along with our prices making this store a great money saving institution for you. We own and operate 10 shoe stores in Pennsylvania, our method of doing business on the quick sale small profit plan and giving you the best possible prices. Buying in large quantities securing all the discounts and selling for cash and making no deliveries avoiding unnecessary expenses thus giving you the advantages to be had by trading with us. We guarantee satisfaction or refund your money on any purchase at any time. Watch for our opening announcement, it will be a great saving to you.
And this from 30th September 1916:
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