These are game tokens that can be flipped between a "+" side and a "-" side. I use them for Magic the Gathering +1/+1 and -1/-1 tokens or Fate free invocations (friendly/hostile) but they can also make a nice d2 or whatever else you can think of.
There are 4 pieces, the inner and outer piece for the plus side and the inner and outer piece for the minus side. Insert the inner plus face down into the outer plus, lay the inner minus face up on top, brush a light layer of cyanoacrylate on top (except the exposed minus symbol) and sit a weight on it for about 30 seconds. Voila!
You can print the outer and inner pieces as different colors, or print the outer plus and inner minus together (I called it "light") and the inner plus and outer minus in a different color ("dark"). Or if you're really ambitious, you could use 3 or 4 different colors.
The tokens are 25mm x 4mm but I've set them up for Customizer.