On our recent visit to Santa Barbara, California, we climbed the steps to the roof of the courthouse clock tower to take in the view. The above device was visible on the way up, through a large plexiglas window. No sign or placard offered an explanation. On the way back down, I saw it again and realized what it was.
Here are two of the views from the roof (the courthouse and grounds occupy an entire city block).
Answer: It's the clock! The tower has a clock face on each of its four sides. You can see that the clock mechanism has an arm extending out to each wall to drive the clock hands.