We ran into a guy at Berea, OH with Pennsylvania plates that read SD70MAC. That's what got us thinking.
MI SoS has a utility to allow you to see if what you want on a plate is available. It doesn't approve anything, nor guarantee you can get it. But, it at least allows you to see if what you want is available.
As an aside, I found another use for that utility. I have a bunch of 1/18 scale Die Cast vehicles. What I did was type in a bunch of random letters and numbers, and then save the resulting GIF image. Using an image program, I resized it down to the size of where the plate would go on the vehicles.