A coaster for your radioactive beverages. 10 cm in diameter, 5 mm thick.
For printing in two colors, look up how to "pause at height" and change filament part way through. You can change colors after 2.0 mm, but before 3.0 mm, for best effect. (I chose to change colors at 2.4 mm.)
Probably best to stick to cold beverages.
Update, 7/5/18: I changed the design slightly to conform to the standard proportions of the radiation warning symbol.
Monoprice Maker Select V2.1