I saw this a long time ago, I guess when the design was announced, but I hadn’t heard they were actually in circulation now. Granted, I haven’t spend much time in the UK, but I think I would have noticed them when I was there a few years ago.
Each coin between the penny and the fifty pence piece features part of an image. They can be put together like a puzzle to create the Shield of the Royal Arms. The pound coin completes the set with the full shield.