Mi3Wheeler, I was riding already when the Michigan helmet law went into place back in 1967. A guy I knew was a State Partol and he caught me about two blocks from my house riding without my helmet. He politely told me to walk my bike home and put on my helmet. What a bummer that was...
As far as cycle training for the endorsement of M on your license may be tough if you do not ride a two wheeler. Here in MO they do not allow three wheelers into the training courses. Most have their own bikes for training, but some county parks do training and you use your own bike. In these cases they allow scooters to be use by trainees in the course.
I'm not sure how one would go about getting the M without riding a motorcycle.
I've heard here that some have gotten their M by riding trikes, but I think it's boils down the location and the official overseeing the ride test.
When I got my M back in 1967, all they did was ask if I had more than 1k miles of riding, which I did. That's all it took back then.
Good luck with your M.
