Here's a recently posted series photos of a World War II 4"x5" tempered glass ESM/1 emergency signaling mirror
and the instructions on the box.

Click on any photo for a larger view. Find the "full size" link on the resulting page to see an even larger view.











( For more photos of old emergency signaling mirrors, there's my photo gallery, too.

http://www.richard-fowell.fotopic.net/c1663439.html

Similarly, there's a "full size" button
if you want to see photos even larger than the ones resulting from clicking on the thumbnail photo.)