IEC 60534-5 Ed. 2.0 b:2004, Industrial-process control valves - Part 5: Marking

specifies mandatory and supplementary markings of control valves. Some mandatory markings may be inappropriate for some valves of special design, and some supplementary markings may be appropriate only to specific types of control valves. It is recommended that the marking of all valves conform to this standard whenever possible unless otherwise agreed between the manufacturer and purchaser.