Special Handling Stamps
On April 11, 1925, the US Post Office issued its first Special Handling stamp, #QE4.
The US Postal Service Act of 1925 clarified what made up the different classes of mail. Everything that did not fall into the first two classes of mail (written matter and periodical publications) was divided by weight. If it weighed less than eight ounces, it was third class, and if it weighed eight ounces or more, it was fourth-class mail.