I try to stay somewhat prepared for disasters of many kinds. I keep some things handy to throw together in case we need to leave home quickly. I have some things that are handy for survival or for camping and one of the things I've lacked was a metal signal mirror. They are not very expensive to buy but I had some old computer Hard Drives laying around that needed to be erased and or destroyed to prevent data recovery from them. I decided to keep the platters from inside the drives to use as signal mirrors. Here is a brief guide to making your own.
Here are two hard drives with a 3 & 1/2 inch floppy disk for size comparison. Notice the screws around the edge of the case and some are under the label. I remove ALL labels, stickers, and screws when dismantling a hard drive.
Closer view of one hard drive. Notice where two screws under the label were removed.
The shiny metal platter inside the case. Remove all screws in the middle hub and those holding other mechanisms in place. There are two magnets inside the case that may give some resistance to removal. Try not to scratch the platters but you may need to be forceful with other parts.
Here are two platters that I removed from a computer hard drive. Your drive may have only one platter for it may have more. Your platters may also be larger or smaller. The platters are made of metal and not easily broken like a glass mirror. I keep mine inside a plastic sandwich bag to keep them from getting too many scratches while camping.
Here is one magnet from the drive I dismantled.
I placed the platter on the magnet and moved it around on both sides to completely erase any data on the platter before I use it as a signal mirror.
Hold the platter in one hand, shine the sun's reflection onto the other hand between forefinger and thumb held to form an L. Using this method you can easily aim your signal spot.
Here you can see my signal spot on the larger tree about the height of the farside curb. To get someone's attention at a great distance, simply move the spot back and forth across their face. You may not be able to see the spot at a large distance but you will still be able to see it on your hand and you can move the mirror back and forth to make the spot move across your hand and the gap between your finger and thumb.