So where does the legend of the equinox and eggs standing up come from? According to the excellent Bad Astronomy: Misconceptions and Misuses Revealed, from Astrology to the Moon Landing "Hoax" by Philip Plait, the myth's introduction to the Western world comes from a Life magazine article entitled "The Mystery of the Upright Eggs Dissolves War Tension in China" published on March 19, 1945.
The article states that the local Chinese believe eggs can stand up an hour before and after the start of Spring. However, traditional Asian Spring is not the same as solar/Western Spring. Traditional Asian Spring, Lichun, occurs around February 4th or 5th. Lichun is based on the sun's location in the sky, unlike Western spring which is based on the tilt of the Earth.
The myth remained little known until neopagan and artist/activist Donna Henes obtained media notice for her public egg balancing acts for "world peace." The event was soon picked up by educators and the public who did not know the truth.