So, what coat of arms does St. Michael bear? When he’s dressed as a knight, he has the chance to display arms on his shield, and perhaps also on his breastplate. Sometimes he holds a banner, although this does not necessarily display his personal arms.
Unfortunately, at this point, no clear patterns have emerged. Here are some rough groupings:
1. “Michael” means “Who is like God?” with the implied answer, “No one.” Thus, St. Michael can bear a shield bearing a Latin form of his name as a motto: Quis ut Deus?
2. As a Christian warrior, it is only natural for Michael to bear a cruciform shield.
2a. Oftentimes, this shield is simply St. George’s red cross on white.
2b. Red and gold are also seen.
2c. Also gold on gold!
2d. Sometimes charges appear in the quarters.
2e. A Russian Michael bears a Russian cross:
3. Several shields aren’t heraldic at all, but are simply blank and/or decorative and/or functional.
4. Many shields feature rays of light or flames.
5. A couple of shields bear an escarbuncle, which is a charge derived from the way a shield is constructed.
6. St. Michael occasionally bears a shield of one of his votaries – in this case, the king of France.
7. I found one that seems to be covered in feathers, like Michael’s wings.
So as you can see, unlike with St. George, who is almost universally identified with Argent, a cross Gules, artists of St. Michael could get quite creative with his coat of arms. If this has any meaning, I assume that it’s because St. Michael is even more heavenly than your average warrior saint, and not constrained by any heraldic rules.