This is a set of three mail stickers of Do Not Stack by Alaska Bunguten, a little stationery shop in Gift Prefecture in Japan who is known for its fun original stationery.

The picture shows what you should not do with a note at the bottom.  In this sticker, a man puts items on items, and at the bottom it says do not stack.

* Measurement: 5cm x 6.5cm (2"x2.5")
* Quantity: 3 Stickers
* Vendor: Alaska Bunguten
* Made in Japan