Once again, that's what I thought too. But I have the drill sheet right here in front of me, and it says "BC logo = the location of the preferred spin axis..."
On the ball, it does look like the "B" part of the logo could be an "R," which might make more sense because that's the name of the core, but it's not. If you think about it further, you'll wonder why they would call the mass bias the robo core.