The attached 7 page article is both the most detailed article, and describes the most thorough signal mirror testing, that I've seen.

It describes the evolution of signal mirror sighting methods to the use of retroreflective aimers, and the test results that caused the US Navy to switch from the "rearsight" method (still common in lifeboat mirrors to this day) to retroreflective aimers.

I obtained this through the kind offices of the US Coast Guard historian.

A complementary overview of signal mirror development across this period (with lots of color photos) may be found here:

http://www.usmilitariaforum.com/forums/index.php?showtopic=2412