> To listen, go to bostonglobe.com/soundtrack. A friend recently returned from the Registry of Motor Vehicles branch in Chinatown with a question I couldn’t answer: When you take a number, why does it have a letter attached to it? You don’t just get a ticket with, say, 195. It says A195 or C195. Is this some kind of Disney World-esque line-management technique, so people don’t realize they’re waiting in one big queue? Turns out the letters actually mean something. On a recent Monday morning, I stopped by the Chinatown branch — the state’s busiest, drawing 1,500 to 2,000 customers daily — to check it out. As an automated female voice droned on with that day’s numbers, branch manager Robbin Hatton explained the system. On the first floor, which handles registrations, the letter A is for people seeking new registrations. F is for registration renewals, and D is kind of a catchall. On the second floor, which handles driver’s licenses, B means you’re getting a new one, C is for those taking exams, and I is for license or ID renewals. At 25 minutes, the average wait time is pretty good. It doesn’t take much to get jittery, though. One guy, who I’m guessing had a paperback copy of The Trial tucked in a pocket, asked if I’d heard any “I” numbers called. He hadn’t and was starting to worry.