Why is "Z Grill" trending?

Wikipedia Overview

The Benjamin Franklin Z Grill, or simply "Z-Grill", is a 1-cent postage stamp issued by the United States Postal Service in February 1868 depicting Benjamin Franklin. While stamps of this design were the common 1-cent stamps of the 1860s, the Z-Grill is distinguished by having the so-called "Z" variety of a grill pressed into the stamp, creating tiny indentations in the paper. Although the 1-cent Franklin Z-Grill is generally cited as the rarest and most valuable of all US postage stamps, the 15-cent Lincoln Z-Grill is just as rare, also with only 2 known to exist. The 10-cent Washington Z-Grill is scarcely less rare with only 6 known to exist. First production runs of Z-Grill process were made of the common Z-grill denominations - the 2-cent Jackson, 3-cent Washington, and 12-cent Washington stamps. The earliest known postmarks of these Z-grill stamps date from January 1868. Then in February 1868 three other denominations were printed with the Z. Grill, the above mentioned 1-cent Franklin, 10-cent Washington and 15-cent Lincoln stamps. These three denominations were only in production for a short period of time with only about 1000 of each being printed before production shifted to the F-grill – resulting in the rarity of these 3 stamps.