omega is the symbol of choice for angular frequency, which is very related to pi, as angular frequency = 2 pi frequency (there is another 2 pi for you right there).
That's omega in its minuscule form. I was referring to its majuscule one.
Oh, I assumed that "omega" is minuscule, and "Omega" would be majuscule, just like in LaTeX. That's why I started the sentence with a small letter. I missed your mentioning its circular shape.