Sir Terry wrote “the Post office began to sell them already affixed to envelopes which were printed with the warning in red: Do Not, Repeat Not Lick, and signed by Assistant Postmaster Groat. There are fewer than a hundred of these known to be in existence.” In fact there were 99, with eight different addresses. The were two each addressed to Moist von Lipwig and Havelock Vetinari, and one each to Sir Samuel Vimes, Reg Shoe, Doctor Whiteface and Mr Slant. Two of these are actually zombies. The envelopes are the single sheet, fold and tuck in type used often in Ankh-Morpork. I am not sure but I believe they were empty. Each is stamped with a Postage Paid Zombie stamp, which cancelled with an AMPO frank. I very much doubt that anyone has steamed a stamp off to check that the yellow and red underprint had been applied. Each is addressed in a different fancy cursive handwriting.