In my case, the icon for the prototypes will be the same as for the other coins sharing the same name. It would be easy enough to give a unique coin its own icon, but Groundspeak would charge $150 and that is more than I want to spend. However, if a customer wanted an icon to go along with a unique coin, I would provide one, given that they paid for it.
I said this because in my case, the samples have an icon, and the versions minted has his own icon.
Edit to add: Really, ...my design has three icons!!