Runic letter Os

It is an Old English rune for the o sound.

This Os rune belongs to the Futhorc, the Anglo-Saxon runic alphabet. In the Old English Rune Poem, the name ōs is explained through the mouth, which gives speech and supports wisdom. Scholars also connect the older Germanic name with a god, often identified as Woden or Odin; the poem's wording has more than one scholarly interpretation.

So “wisdom rune” is a useful shorthand for the poem's image, not a complete account of the name's history.

Where did ᚩ come from?

It developed in the Anglo-Saxon Futhorc from an older Germanic rune.

Its closest historical relative is ᚨ, the Elder Futhark rune conventionally called Ansuz. The Futhorc adapted that inherited rune for Old English, where ᚩ represents o.

Runes appear in Christian as well as pre-Christian settings: the coffin of the Christian saint Cuthbert, from around 700 CE, bears an inscription mixing runes with letters from the Roman alphabet. The Old English Rune Poem gives the rune a riddle-like explanation, but its sole surviving manuscript witness was destroyed in the Cotton Library fire in 1731.

Is ᚩ a magical symbol?

Not by itself: it was an Old English letter for o.

Runes appear in religious settings, but the character alone cannot tell you what a modern sender believes. A standalone ᚩ may suggest runic, Old English, pagan, or fantasy styling; the surrounding message gives that impression its context.

Name the poem or historical letter if that is what you mean. On its own, the glyph leaves its modern significance open.