Thump.
Moist looked down at the piece of paper. Smudgy red letters chipped and worn, spelled out: 'Ankh-Morpork Post Office'.
'That's right, sir,' said Groat, waving the heavy metal and wood stamper in the air. 'I bang the stamp on the ink pad here, then bang it, sir, bang it on the letter, There! See? Done it again. Same every time. Stamped.' 'And this is worth a penny?' said Moist. 'Good grief, man, a kid could forge this with half a potato!'
'That was always a bit of a problem, sir, yes,' said Groat.
'Why does a postman have to stamp the letters, anyway?' said Moist. 'Why don't we just sell people a stamp?'