The $1 Clacks Mail stamp allows people to pre-pay to send a Clacks message, and avoid the queues - though you may have to queue to buy the stamp. They were printed in sheets of 20, with a sport showing a blank light window. You may recall, from Going Postal that the clacks operators are a pretty tight knit group. When one of their number dies, like John Dearheart, they keep the name alive by including it in a GNU message as part of the overhead - the non-message part of the transmissions. A close look at the print tape on this stamp shows GNU TP.