The Aikidōkan Crest

tomoe (巴 "circular, whirl shaped"): A classic Japanese pattern that originally is related to the belief in dragon deities. As such it is said to summon water and is therefore often used as a protective charm against lightning and fire on Shintō shrines' roof tiles. Tomoe patterns are found from ancient times in many parts of Central Asia and elsewhere, for example, on bronze vessels of the Scythians. The pattern appears in many variations in Japanese family crests, the one used here is the "triple, right-handed whirl in a circle". Better known, of course, is the variation as yin-yang symbol, the black and white double whirl.
This symbol was chosen for several reasons as Aikidōkan's crest. First, it displays very nicely the typical circular or whirl-like movements in Aikidō. Secondly, its use as a symbol of protection against lightning and fire implies at the same time its significance as a protective symbol against danger and violence, just like the character bu (武) in budō (武道 the "militant way", the martial arts) is made up from the characters for "to stop" and "halberd", meaning therefore figuratively "to put an end to violence".
At Aikidōkan the tomoe crest furthermore signifies the dialectic of spirit, technique and body (心技体 shin-gi-tai), as in Aikidō thesis and antithesis of body and mind are reconciled and transcended through practicing the Aikidō techniques. (See also the article "Aikidō is ... Dialectics of fighting".)

(Author: Max Seinsch)