Coptic letters/numerals.
Coptic refers to a language of Egypt. It did not exist as a written language until perhaps 200 AD.
The Gospel of Joseph of Arimathea was written in Coptic, however some sceptics purported that it was a hoax.
A parchment dated from at least the mid-13th century and kept by Paolo of Genoa had writing in the Coptic alphabet, appearing to be some sort of cipher.
Marcus Brody had tasked Indiana Jones to translate a parchment for him in 1938.
Behind the scenes[]
The package of Indiana Jones and the Last Crusade: The Graphic Adventure contains a "translation table" with combinations of Greek and Coptic characters. These form the code that Indy must show near the beginning of the game, although they are not identified as Coptic in dialogue.
The bar above each letter signifies that they are not letters of a text, but they are characters with a numerical value (eg. A=1, B=2 etc).
