My grandma was responsible for getting me started in collecting U.S. stamps. She would send me about $5 of face value plate block stamps for my birthday each year. Stamps in the U.S. used to come in sheets of 50? and each sheet was numbered. A plate block was the corner 4 stamps that had the number attached to them. The U.S. no longer has lickable stamps. they all come on a role or sheet and have self-adhesive.
Interesting post. Thanks for bringing back the memories.