The ying and yang is perhaps the most perfect symbol, both the positive and negative
shapes are in balance and form a unity of opposites. Black and white (male and female, etc.) are equal partners.
Symbols, abstract or representational, should convey one strong characteristic,
such as expansion, growth, strength etc. Idealy, they should be as simple as a letter of the Latin alphabet.
The strength of a symbol can be tested at small sizes usually on the business card.