In the U.S., container manufacturers and reconditioners who certify packagings as suitable for use in shipping hazardous materials (a.k.a. "dangerous goods") must mark their packagings with their name and address, or a symbol registered with the U.S. Department of Transportations's hazmat office. In he place of symbols, the DOT issues what are referred to as "M" numbers. (In the past, they issued "R" numbers, most of which are still valid and in use. However, since 1994, all applicants receive only an M number) "M" and "R" numbers are typically four numbers folllowing the letter M or R.