KGVI registered letter envelope

The blue lines (and sometimes red) originated as lines where once string was tied, it tied around all 4 edges, then knotted in the centre, and hot wax applied and a seal upon it, pressed into it, providing evidence the parcel had not been opened.

History.........

www.the153club.org/khaldun2.html

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."

I found this text in wikipedia

The registration of letters as known today was introduced in 1841 in Great Britain. The letter had to be enclosed within a large sheet of green paper. The green sheet was addressed to the Post Office where the recipient lived. The green sheet was then used as a receipt and was returned to the office of origin after delivery. On 1 July 1858 the green sheet was replaced by a green silk ribbon and shortly afterwards by a green linen tape. In 1870 the tape was replaced by green string. On the introduction of postal stationery registration envelopes in 1878 the string was replaced by printed blue crossed lines. The blue crossed lines have survived on registered letters to the present day

I remeber as a kid in Ireland the local post office which was attached to the local store had a blue wax pen just like a crayon that cjd mentioned.
It had a ball on the end of it, one of those things that stick in your head.