Normally, the king would declare and sign a proc stating that anything signed by his secretary's "unforgeable" signet was to be respected as well. The secretary could delegate authority to others in turn.
Well turns out that one of the signets in the chain of trust was just a picture of a "four" that anybody could have forged, but nobody noticed because in all of the ceremony and stacks of parchment with wax seals, nobody actually checked if the signet was secure.