A few post offices are now making stamps that bear a sort of matrix code on them, like this:
Each code is unique, and as it goes through the postal system, they’re able to mark that code as “used”. If the stamp is washed or otherwise copied after being used, the system is able to detect that the code is no longer valid, and thus reject that piece of mail. It also allows the post to potentially track the journey of that stamp through their system.
I’m curious to hear what people think of these codes, which are probably here to stay. Do they bother you at all? Does it change anything for you in the mailing or collecting experience?