46 CFR §50.10-30

1. (a)The Coast Guard number means that number assigned to boilers and pressure vessels by the Officer in Charge, Marine Inspection, who makes the final tests and inspections.
2. (b)The Coast Guard number must be stamped on the nameplates of boilers and pressure vessels.
3. (c)The Coast Guard number is comprised of the following:
   1. (1)Three capital letters which identify the office of the issuing Officer in Charge, Marine Inspection (see table 1 to § 50.10-30); followed by,
   2. (2)An OCMI serial number, by which the particular boiler or pressure vessel can be identified; the first two digits of which will identify the calendar year the number was assigned.