"Much of Sigma Chi's heraldry is inspired by the legendary story of the Emperor Constantine from the Battle of Milvian Bridge against Maxentius. Notably, the White Cross and the motto "In Hoc Signo Vinces" are evidence of the Constantine link. Although many of the symbols of Sigma Chi relate to Christianity, Sigma Chi is not a religious or Christian fraternity." -- The Norman Shield [Reference manual (pledge book) of the Fraternity]
The Crest - The Crest is a Norman Shield of blue bearing a white Sigma Chi cross, the shield being surmounted by a scroll and a crest of an eagle's head holding a key. The public motto, "In Hoc Signo Vinces" is placed below the shield on a scroll. The meaning of the motto is, "In this sign you will conquer." It is pronounced: "in hoke sig'no win'case."
The Flag - The flag is rectangular, the length being one and one-half times the width, the upper half being blue, the lower half being old gold, with a white Sigma Chi cross standing upright in the center and parallel to the lesser sides.
The Seal - The Fraternity seal is circular. Around the top of the outer edge is the name Sigma Chi Fraternity, and at the bottom are the numbers 1855. The central portion contains seven stars and a seven-branched candlestick.
During my search for pictures, I found this and thought it was nice to see how the various symbols are used on each.