To photograph edges, first get yourself an old fashioned torch. One with a central bulb and, more importantly, a reflector.
Take out the reflector and throw the rest of the torch away. The new LED versions are much better anyway.
Standing the reflector so that from above, it becomes a dish place your edge marked piece as horizontally as you can in this bowl.
As you're lowering it in, check that you can read the edge description. i.e. it's not upside down. This makes the later stuff easier.
Now as you hover over the coin with your camera at an appropriate angle you'll see the edge inscription reflected in the bowl you have created, only now it will be in mirror writing.
Take your pics and then reverse them out in your favourite editing software.