The second digit identifies the specific vehicle's manufacturer. It's often the first letter of the manufacturer's name, such as B for BMW vehicles.
Since some characters can stand for multiple manufacturers, the third digit combines with the first two to indicate the specific manufacturing division. For example, JM1 can designate Mazda, while JMB can designate Mitsubishi. The first three digits together are known as the World Manufacturer Identifier (WMI).
Here are some of the commonly used second digits: