I made these cookies for Scot's Aikido seminar. Here is the meaning of this symbol and of Aikido.
yin and yang=
(Chinese philosophy) the two fundamental principles, one negative, dark, passive, cold, wet, and feminine (yin) and the other (yang) positive, bright, active, dry, hot and masculine. The interactions and balance of these forces in people and nature influence their behavior and fate.
Aikido, is a Japanese martial art developed by Morihei Ueshiba as a synthesis of his martial studies, philosophy, and religious beliefs. Aikido is often translated as "the Way of unifying (with) life energy"  or as "the Way of harmonious spirit."  Ueshiba's goal was to create an art practitioners could use to defend themselves without injuring their attacker.
Aikido emphasizes joining with an attack and redirecting the attacker's energy, as opposed to meeting force with force, and consists primarily of body throws and joint-locking techniques. In addition to physical fitness and technique, mental training, controlled relaxation, and development of "life energy" or "spirit" (ki) are emphasized in aikido training.