The sig rune (or Siegrune) symbolised victory (Sieg). The names of the ᛋ-rune (on which the Siegrune was based) translate as “sun”, however, von List reinterpreted it as a victory sign when he compiled his list of “Armanen runes”.

It was adapted into the emblem of the SS in 1933 by Walter Heck, an SS-Sturmhauptführer who worked as a graphic designer for Ferdinand Hoffstatter, a producer of emblems and insignia in Bonn. Heck’s device consisted of two sig runes drawn side by side like lightning bolts, and was soon adopted by all branches of the SS – though Heck himself received only a token payment of 2.5 Reichsmarks for his work. The device had a double meaning; as well as standing for the initials of the SS, it could be read as a rallying cry of “Victory, Victory!”. The symbol became so ubiquitous that it was frequently typeset using runes rather than letters; during the Nazi period, an extra key was added to German typewriters to enable them to type the double-sig logo with a single keystroke

Blatantly ripped from wikipedia