It's been talked about, like this one, or this one , but I don't know of anyone who actually has one.

I saw your scan of your stamp, and I would advise changing it. When you put the URL of all 3 tracking sites on the note, people will either:
a) just go to the first one on the list
b) have no idea what it is for, and do nothing, or
c) think that they have to go to all 3, and do nothing