They could use them to tell if/when the buildings have moved.

The need for a prism for accurate EDM is outdated, my LiDAR scanner can get sub 3mm accuracy w/o a reflective target, and my total station can do darn near 1mm ranging on anything – prism or paper.  The only reason to use a prism with modern equipment is if you’re going fully robotic target acquisition. Though they may be using the “red” target simply for off-axis aquisition. Those flat targets are only really appropriate for use when your line of sight is perpendicular to them – use them from a side angle and the width of your EDM’s spot becomes a factor as you’ll get returns from multiple distances.

EDIT: Though I swear I can see the word “Leica” on the top targer. Odd in that Leica and Trimble equipment are rarely seen to mix in the wild.

At 10 feet those are for a lower reference point. Look very carefully way up on the building, they should have installed a second set at the 7th-ish floor or so.

Look around the area.  Are there any new developments within a block or so? If so, if anybody is driving piles or shoring beams, then a monitoring program of the surrounding area will be warranted.  Even small shifts if the soil can mean big issues, especially in buildings that old. 

Of course this is San Francisco you’re talking about, it could be for fault movement, but just to say, these kind of monitors are hardly restricted to that kind of program.    

[Edit- Above poster mentioned a new subway tunnel is being dug in the area, I can nearly guarantee that's exactly what it is, and that said tunnel contractor received the invoice for the installation and monitoring of these things via laser total station]