3M makes a product called VFLUO that is retro reflective material. It comes in approx. letter sized peel and stick adhesive backed sheets, or stickers. I got a couple of the sheets (black) of the VFLUO (or something very similar) years ago before they called it that, cut some strips and made a chevron on the back of my helmet. I have had a number of folks tell me that it is very visible and attention getting it is. The black strips look like white lights when headlights hit them.
I have put it on my helmet, saddlebags when I had black ones, back of a sissybar pad, a strip across the bottom of the rear fender like a trim piece, ...
Search Amazon for "retro reflective sheet". Sheets and stickers will be listed for the 3M product and other brands.