A bit about me, since I just joined the forum:

I'm more into mirror signaling than survival per se.

The white spot in my avatar is not the sun (which was off to the right) but rather a view of the "virtual sun" ("fireball" / "bright light spot") created by the retroreflective bead aiming mesh of a glass signal mirror.

The U.S. military switched to retroreflective aimers on their signal mirrors from their (already deployed) system of "rearsight" mirrors after finding that even the primitive first generation of retroreflective aimers was 2.5 times as effective as the rearsight method for the (admittedly difficult) task of signaling from a bobbing liferaft to a moving plane.

These results and this decision was announced in: "Signaling with Mirrors: Reflex-Button Type of Mirror Adopted for Navy Survival", Naval Aviation News, 15 Sept 1944, pp. 32-33, which can be downloaded from the official government site here: http://www.history.navy.mil/nan/backissues/1940s/1944/15sep44.pdf

I have a site with some photos of old military signal mirrors and links to various pieces of signal mirror history here:

-R. Fowell
A signal mirror should backup a radio distress signal, like a 406 MHz PLB (ACR PLB) (Ocean Signal PLB)