High Gallifreyan

High Gallifreyan was the ancient language of the Time Lords. It was not known by many; by the Doctor's era, it was virtually extinct.

The written form of High Gallifreyan resembles, to human eyes, a mixture of Greek letters and mathematical symbols. (DW: The Five Doctors)

Inside the Tomb of Rassilon in the Death Zone on Gallifrey, an old rhyme was written in "Old High Gallifreyan" which explained the outcome of the "Game of Rassilon". (DW: The Five Doctors)

Within the Doctor's rooms on Gallifrey there was a painting of a woman, holding a scroll with the words "Death is but a door" written in High Gallifreyan. (PDA: The Infinity Doctors)

The First Doctor wrote his Five Hundred Year Diary in High Gallifreyan to make sure no one could read it. (DW: The Power of the Daleks)

In addition to written High Gallifreyan, two other forms of written Gallifreyan have been seen:
 * a vaguely Arabic-looking script, in a letter written by the Doctor to warn the High Council of impending danger (DW:The Deadly Assassin). This writing system is probably more appropriate for everyday communications, such as letters.
 * a complex system of interlocking circles. This writing system is used by the TARDIS' output screens, and is the one seen in the notes that the Doctor scatters around the TARDIS console room, so it may be a specialized system optimized for communicating time-related concepts or TARDIS settings.