Failure to register the handgun is a civil infraction under MCL 28.422
Carrying any gun concealed on your person, off your property or in one's car violates MCL 750.227. A gun carried in the trunk, unloaded, in a wrapper/case would be an exception under MCL 750.231a. The gun must be registered under 28.422 to get this protection. This is the felony.
Mere possession of an unregistered gun does not appear to be a felony under MI law. It can be kept in your home, place or work or on land in your possession without incurring a felony. From a technical reading of 750.227, you could probably open carry an unregistered gun, off your property, without incurring a felony. In fact a "dagger, dirk, stiletto, a double-edged nonfolding stabbing instrument of any length" is legal as long as it is in your home, work place, or land possessed by the individual.
As for the MSP bulletin. It says quite clearly that the individual "
may" be in violation of 750.227 (may was even underlined in the bulletin). The problem is that 28.231 says that an exception to 750.277 is "...a person while transporting a pistol for a lawful purpose..." with the old "to and from" rules as examples of lawful purpose, but not the only lawful purpose. Unless the prosecutor would be will to argue that open carry of a firearm is not a lawful purpose, that charge would be DOA. Open carriers should have a CPL as there are so darn many places that would be off limits to open carry without one, that it is practically required if you are in a city.