Stephen Hawking has been buried in Westminster Abbey (London, England) next to Isaac Newton. If his wishes become real then maybe you may see this formula too in Westminster Abbey.
This formula of Stephen Hawking gives you the entropy of a black hole. S is the entropy. A is the surface, c is the speed of light etc
One of the good things of this stamp is that you can see too the year 2018, so the year when Stephen Hawking was buried in Westminster Abbey.
You can also choose the formula printed in cyan color. In cyan? What has this to do with this formula? Well, it has nothing to do with the formula of Stephen Hawking. It just has to do with the color very oft used by Espanyol de Cornella in its designs.