It's like a special endorsement you have to have to be able to operate a motorcycle, legally.NY Stater here - what does motorcycle endorsement mean?
Just as you need a Class C license to operate a certain size of truck.
And the list goes on, it's a license for operation of certain classes of vehicles, like Semi's, Motorcycles, Chauffer, and the list goes on.
It also includes Limo driver, cab driver, bus operator, have to have the endorsement to prove you know how to operate that type of vehicle.