These kamon were originally modeled after tsurumaki, a leather, ring-shaped spool used to reel bowstring. The tsurumaki was an essential part of a samurai's battle gear. Later, the design came to be called janome simply because of its resemblance to a snake's eyes. It was usually adopted by samurai families for its warrior symbolism.
(From 'Family Crests of Japan' by ICG Muse, Inc.)
Drawing method of Snake eye
Drawing method of Trisected snake eyes in threadlike ring