How to use a double sided mirror. This will be hard to describe...easy to do, but hard to describe.

Assume the target and the sun are both in front of you. Hold the mirror up in front of your face and look in the "back" mirror for the spot caused by the sun coming thru the hole.

Now line up the reflected spot with the hole, and the target. You will have the sun reflected directly on the target and will be able to hold it there.

It is a bit more complicated if the sun is low behind you and the target is in front of you. Then hold the mirror sort of flat and look for the sun spot on your hand. Line up the sun spot, hole and targer and you got it. Takes a bit of practice (about 10 minutes) to get it, but simple thereafter.

Having been on both ends of a signal mirror, it is important to be able to hold the mirror on target. Under some conditions (at sea or over melting ice or snow) there are thousands of sparklie reflections. Finding the right one is a real problem. After a bit, the observer may notice that one light is not flashing but steady. If you can't hold the mirror on target under these or similar circumstances, the mirror won't look much different than the snow melt or wave reflections.