Excellent question Lucky.
It is a carry over from times long past when letters were sealed with string and wax as a guarantee that they had not been opened or read.
Ergo:
On the Origins of Registered Post—by Ibn Khaldûn (1332-1406)
Ibn Khaldûn, the Arab philosopher, historian and politician, was born in Tunis in 1332. His major
work is the Muqaddimah or An Outline of History, from which the following translation is taken.
On the origins of registered Post:
"It is also possible to impress a seal upon some soft substance, so that the letters of the legend
appear on that substance, and to place the substance (with the seal impression) on the knots (of the
strings with) which letters are tied, and upon places for deposits (such as storehouses, strong boxes,
etc.). The first to introduce the sealing of letters, that is, the use of signature, was Mu'âwiyah. He
also introduced the ministry of the seal. It is composed of the secretaries who see to it that the letters
of the ruler are expedited and sealed, either by means of a signature, or by tying them. Letters are
tied either by piercing the paper and tacking (the letter) together (with string), as is the custom of the
secretaries of the Maghrib, or by glueing the top of the sheet to the part of the letter over which the
top is folded, as is the custom of the people in the East. Over the place where the letter is pierced
and tacked, or where it is glued, a signature is placed. It guarantees that the letter has not been
opened and that its contents have not been read. The people of Maghrib place a piece of wax where
the letter is pierced and tacked, and seal it with a seal upon which some signature is engraved for
use in sealing, and the engraving is impressed upon the wax. In the old dynasties of the East, the
place where the letter was glued was also sealed with an engraved seal that was put into a red paste
of clay prepared for that purpose. The engraving of the seal was impressed upon the clay. Under the
Abbâsid dynasty, this clay was called 'sealing clay'. (The use of) the seal was peculiar to the ministry
of correspondence. In the Abbâsid dynasty, it belonged to the wazir. Later on, custom differed. It
went to those who were in charge of (official) correspondence and the office of the secretaries in the
(various) dynasties. In the Maghrib, people came to consider the seal ring as one of the royal marks
and emblems. They made artistic seal rings of gold inlaid with gems of hyacinth (ruby), turquoise,
and emerald. The ruler according to their custom wore the seal ring as an insignia."
http://www.the153club.org/khaldun2.htmlI am unsure of the significance of the colours, but here is an Aussie printed:
Posted 03/18/2010 11:15 am
