Priceless Paintings from W7

When I went and bought some stamps for letters to Australia and the US at the post office the other day, the post office guy handed me the usual sheet of free "Air Mail” stickers to go alongside.

We’ve gotten so used to those that I don’t normally think twice. Until today.

Surely, nobody would even contemplate to deliver my letter to Australia or the US by ship or on camelback, should I fail to stick the tiny blue Air Mail adornment onto the envelope.

Would anyone care to tell me the purpose of this sticker, in this day and age?

Thoughts Post Office;