MS registration for Mureş county for list of Romanian counties and registration letters,see en.wikipedia.org/wiki/Template:Romanian_counties_map">here The 31 at the start of the registration is often found on buses in the system introduced in 1966 until 1992, though the old style plates were valid until late 2000 1 to 19 - automobiles, since 1990 all private vehicles, regardless of type 20 - reserved for automobiles, but never used 21 to 30 - light commercial vehicles 31 to 40 - heavy commercial vehicles; buses 41 to 45 - tractors 46 to 50 - motorcycles.