What threw me off was the OP saying the coin is the size of a quarter. As a 2 maravedis, it should be about the size of a nickel.The "R" that I thought I saw to the left of the shield (signifying real or reales) is actually a "B" (Barcelona mint) as shown more clearer in Bramblefind's post.
The image is that of a lion, crowned with scepter and sword with two spheres representing both worlds at his feet. The lion represents the protector of virtue in both worlds--the old and the new, perhaps.
Don....