The three symbols most important to the Baha'i faith are the nine pointed star, symbolizing completion:

the ring stone symbol, so called because it is worn on rings by many believers:

The three horizontal lines represent the three basics of Baha' belief- the world of God, the World of God's manifestation, and the world of man. The vertical bar represents the connection of these worlds, and the stars flanking the glyph represent the Báb and Bahá'u'lláh, the founders and prophets of the faith.

and the "symbol of the Greatest Name:"

This symbol is a phrase, "Yá Bahá'u'l-Abhá," or "Glory of Glories," rendered in calligraphy. "Baha," or glory, is also found in the name of Bahá'u'lláh.

Related Resources:

Baha'i Faith
Baha'i religion at Alternative religions.