A wiki article suggests native indians used mirrors, but I found no real reference.
I found in
a thread elsewhere that the Coast Guard published some interesting information from WWII which suggests that U.S. conceptions may have still been somewhat immature in AE's time, but a war time event may have advanced the idea dramatically -
"...1944 book also suggests a single occurence:
http://www.archive.org/stream/firstfleetthesto011061mbp/firstfleetthesto011061mbp_djvu.txtFull text of "First Fleet The Story Of The U S Coast Guard At War"
The Story of the U. S. Coast Guard at War-
REG INGRAHAM
INTRODUCTION BY SECRETARY OF THE NAVY FRANK KNOX
THE BOBBS-MERRILL COMPANY
Publishers
INDIANAPOLIS NEW YORK
pp. 260-261
"The majority of the Coast Guard's wartime safety measures are based on careful analysis of the experiences and recommendations of a large number of survivors, but a few of them can be traced to individual occurrences.
One group of seamen, for instance, came ashore after a protracted period in a lifeboat and it was discovered they had been overlooked repeatedly by patrol planes.
"We could see the PBY's [Navy flying boats] go by," they related, "but we were unable to attract their attention."
Finally one of them hit on an idea. Taking the bottom of a tin ration can, he fastened it to the blade of an oar and used it to flash the sun's rays back at the planes. This crude heliograph proved effective, too, and soon thereafter the Coast Guard made it mandatory for all lifeboats to be equipped with polished steel signaling mirrors. They are somewhat more elaborate, of course, than the piece of tin can fastened to an oar blade, and each mirror is accompanied by simple instructions for sighting it so as to give the maximum chance of the signal being seen. "
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The text above was also verified by searching each paragraph to verify it as being present in the Google Books online "snippet view" version here:
http://books.google.com/books?id=zRnTAAAAMAAJ..."
I don't think I really advanced this topic, but maybe it can be a useful starting reference for Jeff Hayden or someone to follow-up on.
LTM -