 Also, today is American Zoo Day. There are more than 2,400 zoos in the United States. And it's also National Postal Worker Day, National Postage Stamp Day, recognizing America's 500,000 postal workers. It also happens to be the 177th anniversary of the postage stamp, first issued by the U.S. on July 1, 1847. Before then, you could send lenders cash on delivery.