Here's a better link (with the right photo):
http://www.cbc.ca/news/canada/north/story/2012/07/10/north-inuvik-boaters-saved-pilot-sos.html

It's big country up there. Their boat broke down and they managed to reach a cabin. Nobody knew where they were headed. They painted "SOS" on the boat and used a mirror (probably not a signal mirror, but the story is unclear) to get a pilot's attention.

The pilot's comments are highly instructive:
"When I saw the S.O.S., I knew exactly what it was. But I actually didn’t see the S.O.S. until I was almost overhead the cabin. It was actually, whoever was using the mirror to shine a light — that was the thing that got my attention. Otherwise I never would have seen it from how far away I was," he said.

Szaefer [the pilot] said the light must have been reflecting from four to five miles away.