I have seen signal mirrors from the air and used them many times in all sorts of snow conditions - High alpine in the Rockies, Tundra in Alaska and Canada and Glaciers in Alaska and the Antarctic. They were commonly used for aircraft to find the field parties before lightweight radio's. I am sure that they still work as well today. They are much lighter than a radio.

Respectfully,

Jerry

p.s. I still carry one in the field and let the pilots know that if they don't hear from me to look for it - it is my primary backup.