What is this icon?

[hup_d_dup]

It appears in several places on NASA's Curiosity rover.

I haven't been able to find any radiation or moving parts icons that match this graphic.

Hup

[UDELBR]

The black-and-white calibration badges make it easy for the rover's sensors to know exactly where all its parts are and test to make sure its cameras are focusing at the distances JPL thinks they are. These circles are all over various joints and surfaces of the rover's body

http://tinyurl.com/nhng59j

[hup_d_dup]

Thank you!

Now that you mention it, it reminds me of the registration marks we have used forever in the graphic arts, also to establish precise positioning.