A Klingon mummification glyph was a form of carved pictograph writing used by the Klingons.

During Spock's memory test in 2286, he was asked to identify a particular symbol, which turned out to be a mummification glyph. (Star Trek IV: The Voyage Home)

Background information

The Klingon mummification glyph seen in the fourth movie was identified in the script as coming from the earliest part of the Zanxthkolt Dynasty. The movie was not so specific.

The practice of mummification indicates that Klingons valued the bodies of their dead at some point, in contrast to the attitude shown in the episode "Heart of Glory"; where the Klingon body was considered an 'empty shell' immediately upon death. That attitude, common in the 24th century, also appears to be in contradiction with the funerary customs observed by T'Kuvma and his followers aboard the Sarcophagus ship, as well as the practice of ak'voh. It is possible that the attitudes of T'Kuvma and his acolytes had generally fallen out of favor by the 24th century; ak'voh may represent an ancient and antiquated position that is no longer commonly observed. It might also be possible that only the remains of certain important individuals were preserved. A further hint can be found in "Emanations", where in an unfortunately unfinished sentence Chakotay seems to hint at archeological digs on the Klingon homeworld complicating the picture of Klingons not having burial rituals. At least the ancient ruler Molor might in fact have been mummified, since some entrepreneurs on Maranga IV claimed to have Molor's mummified head on display for a fee of 50 darseks per person. (DIS: "The Vulcan Hello", "Battle at the Binary Stars"; TNG: "Firstborn")