U+16E8 Runic Letter Icelandic-Yr

The Wikipedia has the following information about this codepoint:

Algiz (also Elhaz) is the name conventionally given to the "z-rune" ᛉ of the Elder Futhark runic alphabet. Its transliteration is z, understood as a phoneme of the Proto-Germanic language, the terminal *z continuing Proto-Indo-European terminal *s via Verner's law.

It is one of two runes which express a phoneme that does not occur word-initially, and thus could not be named acrophonically, the other being the ŋ-rune Ingwaz ᛜ. As the terminal *-z phoneme marks the nominative singular suffix of masculine nouns, the rune occurs comparatively frequently in early epigraphy.

Because this specific phoneme was lost at an early time, the Elder Futhark rune underwent changes in the medieval runic alphabets. In the Anglo-Saxon futhorc it retained its shape, but became otiose as it ceased to represent any sound in an Old English. However, possibly due to runic manuscript tradition, it was occasionally used to transliterate the Latin letter X into the runic script.

In Proto-Norse and Old Norse, the Germanic *z phoneme developed into an R sound, perhaps realized as a retroflex approximant [ɻ], which is usually transcribed as ʀ. This sound was written in the Younger Futhark using the Yr rune ᛦ, the Algiz rune turned upside down, from about the 7th century. This phoneme eventually became indistinguishable from the regular r sound in the later stages of Old Norse, at about the 11th or 12th century.

The shape of the rune may be derived from that of a letter expressing /x/ in certain Old Italic alphabets (𐌙), which was in turn derived from the Greek letter Ψ which had the value of /kʰ/ (rather than /ps/) in the Western Greek alphabet. Alternatively, the rune may have been an original innovation, or it may have been adapted from the classical Latin alphabet's Y, or from the Rhaetic alphabet's Z.