Sneaky, SneakyFun with stamps
: "Before 1840, when postage stamps were first used in England, the recipient of a letter paid for its postage. And since the cost was often prohibitively expensive, people began placing small marks and symbols on the front of mail. These codes allowed senders to convey a message to the recipient without obliging the recipient to pay for the formal acceptance of the letter. The loss of revenue from the use of these codes was one of the reasons that the British government adopted the system of prepaid stamps that is used almost everywhere now."