9. Writing System
The writing system, called Mâshur (or Maushur in Zhâburi A), is a variant of Tengwar and function in the same way but is mostly written with a brush. Above is the ring verse Ash nazg durbatulûk etc is written with Mâshur.
Tolkien never stated or developed a writing system for the Black Speech or of Mordor but the Ring Inscription is written in Tengwar. The idea behind Mâshur is just like the Orcs are corrupted Elves Mâshur is a corrupted variant of Tengwar. Sauron used Tengwar to write the Black Speech in the Ring Inscription but a new style was invented were the lúvar (bows) was altered to horisontal lines. The style is inspired by Cuneiform, which is also the writing system used by Hurrian.
In Lord of the Rings Appendix E Tolkien writes that orcs used variants of Cirth:
The Cirth in their older and simpler form spread eastward in the Second Age, and became known to many peoples, to Men and Dwarves, and even to Orcs, all of whom altered them to suit their purposes and according to their skill or lack of it.
But it seems like this did not apply to Mordor by, at least not at the time of The War of the Ring. In the chapter The Departure of Boromir the Uruk-hai of Isengard wore an Cirth S-rune on their helmets
‘S is for Sauron,’ said Gimli. ‘That is easy to read’
‘Nay!’ said Legolas. ‘Sauron does not use the Elf-runes.’
In the chapter The Black Gate is Closed runes are mention in connection to Mordor orcs and other servants of Mordor
They had not come very far from the road, and yet even in so short a space they had seen scars of the old wars, and the newer wounds made by the Orcs and other foul servants of the Dark Lord: a pit of uncovered filth and refuse; trees hewn down wantonly and left to die, with evil runes or the fell sign of the Eye cut in rude strokes on their bark.
Even though Tengwar and Mâshur is not proper runes I still think that ‘rune’ here is just a word better suited than ‘letter’ or ‘character’ and coul very well apply to Mâshur.