Fan sign - what is it?

[rdtindsm]

I am not a huge baseball fan, but usually pay attention during the World Series. I’ve noticed people behind home plate making a gesture with their forearms in a cylindrical motion parallel to the ground.

What is the significance of this? I’ve seen it over the years, Sunday, and tonight (Tues)

 

[BBHMagic]

Clear the bases or hit a home run I'm guessing. Catchers and pitchers do it when they want to run through the signs one more time.

 

[Ry4Cy]

Traveling.

 

[KCClone1]

I always thought they were trying to distract the pitcher but I don't know. What I do know is that I want to punch them all in the face because it is annoying.