This runic sign is called the Wende-Horn. It is a rune binding of the life and death runes – namely the Yr and man runes. Wend is from the Proto-Germanic root *wanđijanan 'to turn'. Wiligut used the Wende-Horn in his own rune row, and many folk associate the rune with the phonetic value ‘mm’.
If we look at the binding of Yr and Man we find that it gives us Yrman – a variation of Irman/Irmin which is the name of the Saxon god of the Irminsul. The Wende-Horn is a runic representation of the Irminsul and the turning of the cycle of time. Unlike Norse cosmology which has nine worlds, Anglo-Saxon cosmology only contained seven. These are the three branches into the heavens, the three roots into the underworld, and the central stave (symbolising Midgard).
The Irminsul with the sacred Sunwheel.
Another clue which links the Wende-Horn to the Irminsul is that Wiligut used a sideward variation of the Wende Horn and used the name Wan and Iring for this rune. Iring is the ‘Milky Way’ and another form of Irmin.
Life and Death