from wikipedia:
The origin of the logo may be traced back to a trip made by the 22-year-old André Citroën to Łódź city, Poland, where he discovered an innovative design for a chevron-shaped gear used in milling. He bought the patent for its application in steel. Mechanically a gear with helical teeth produces an axial force. By adding a second helical gear in opposition, this force is cancelled. The two chevrons of the logo represent the intermeshing contact of the two.