All 50 states require an endorsement. As of 1995 only 2 states did not require one. For some reason Ohio and Iowa come to mind, but I could be wrong. As mentioned before, most state view riding a motorcycle without the endorsement the same a not having a license at all. In Oklahoma, and I'm sure several other states, operating a motor vehicle without a license is a jailable offense. However officer discretion usually kicks in. I would rarely jail someone on that single charge. Add no insurance (which is also jailable in OK) and you were heading to my lockup. Unless you were doing something very stupid, alcohol involved, or “talked yourself†into jail, it would take two jailable offenses for me to haul you in. I think the majority of the officers feel the same way. However there are still those that don’t.
Very many insurance companies will not insure unlicensed drivers or unlicensed riders.
All states vary on the test procedures. Almost all require a separate written test. Some use a skills evaluation (often based on the MSF test, others like Oklahoma, use a regulation compliance test. In OK, they give you a radio receiver to clip on you collar, follow you in a car giving you commands by radio. They are looking for head checks, signals, stops, lane changes, speed, and parking in OK. I guess if you fall you’d fail as well.
I received my license in 89-90 during a time after they started requiring an endorsement. All I had to do was convince the DPS examiner that I had been riding before and they added it on the spot. I was grandfathered in which was stopped here 6-8 years ago. In 2004 when I became an instructor I had to take the motor vehicle written test, the motorcycle written test, and the motorcycle riding test to become a state certified instructor. I have to recertify every four years with state and every 2 years with MSF to maintain my certification.
Quite a few states allow the MSF course to be used as an exemption to one or both tests to get your endorsement. Oklahoma exempts the BRC and ERC graduates from taking the riding test. That itself has increased enrolment in the MSF classes around here tremendously. (and that is a good thing) I think there is a couple of states that require the MSF class (and even pay for part of it). Some state will take MSF class certificates from other states, some will not. Some have a limited list of other states whose certificates are approved.