Historical
IEC 60534-5 Ed. 1.0 b:1982
Industrial-process control valves. Part 5: Marking
Specifies mandatory and supplementary markings of control valves. Some mandatory marking may be inappropriate for some valves of very special design. Mandatory markings shall be located in such a way that markings remain permanently. The location of supplementary marking is also specified.
International Electrotechnical Commission [iec]