That’s exactly it - when a piece of mail with a stamp on it is “canceled” by stamping something on it with ink, yes, that prevents the stamp from being reused, but it is also the sign from the postmaster that the mail may be delivered, having been appropriately paid for.
Aha! I’ve always wondered why office postage meters are called franking machines.
That’s exactly it - when a piece of mail with a stamp on it is “canceled” by stamping something on it with ink, yes, that prevents the stamp from being reused, but it is also the sign from the postmaster that the mail may be delivered, having been appropriately paid for.
The cancellation stamp is a franking mark.