There are different methods of accomplishing this; but this is what I learned back in wilderness survival in scouts. Any mirror works and it is nice to have one designated specifically for this purpose.
My emergency mirror is a small pocket mirror. In the center of this I scratched a small hole in the reflective coating on the back side of the glass as shown in the diagram above. This does not require I mirror larger than a few inches square and in an emergency can be made by everything from a makeup compact mirror to the rear view mirror.
To signal extend one arm making a “V” shape with two of your fingers like an aiming point. With the other hand hold the mirror up to your eye and peep through the hole in the middle.
Through the peephole reflect the light of the son onto and between your extended aiming fingers. All you have to do is take the aiming hand with the light hitting it and sight it on a plane or other location you are trying to signal. If the peephole, your fingers and the light line up on target then they can see you.
Jon
the picture came from http://www.artofmanliness.com/2012/06/14/survival-cell-phone/; they have some good additional ideas.
One clarification: if the center of the peephole, the center of the small shadow cast by the peephole on your fingers, and the target line up, you are on target. Just hitting your fingers with beam of light is nowhere near sufficient.
The beam cast by a signal mirror is far, far narrower than it seems at close range – if you hold a penny out at arm’s length, the head of Lincoln is about the right diameter (or hold up your fingers to the full moon).
There’s a nice photograph illustrating that here: http://www.flickr.com/photos/signalmirror/8422523906/ (Google for “aiming signal mirrors is hard” if the link didn’t work).
However, by putting a small hole in the mirror, as described above, you know where one end of the shadow cone cast in the center of the reflected beam is, and by catching the peephole shadow cone on your fingers, you know where two points on the line of the beam are, and you can line them up with the target.
You can see how reliably the peephole shadow aiming method is working for me to hit the video camera of me at 11 mile range with a CD in the Youtube video: “CD as signal mirror – 11.1 miles”, at http://www.youtube.com/watch?v=xAvw2qLT4dU
For that video, I augered a small hole in the rear of the CD with my pen-knife (the regular hole in the center of the CD is far two large for accurate targeting. Also, the wide “vee-finger” pose is similarly overly broad – I use the “vee-notch” formed by the tips of my index and middle finger held against each other as my sight, place the target in that notch, and flick the peephole shadow up and down across that target.
Here my friend is signalling me at 22 miles with a stainless steel mirror and the same technique. http://www.youtube.com/watch?v=k0_5P1qPFsk
Having said that, it is a lot easier to aim a real signal mirror with a retroreflective mesh aimer, like the two brands sold at REI: the 2″x3″ glass Coghlan’s mirror, or the 2″x3″ SOL Rescue Flash mirror. The retroreflective aimer produces a glowing dot against the sky (the dot is about 3x the diameter of the actual beam), and if you pass the center of that dot back and forth across the target, it’s easy-peasy.
Here’s a series of videos of mirror with retroreflective aimers in use at 0.7, 11.1 and 43 miles: http://www.youtube.com/watch?v=GwCbgQGmID4 .
I appreciate the info. I think I’ll have to improve upon what I learned in scouts years ago and give it a shot.