For containers passing the Volumetric Expansion Method, cylinders should be marked with?

The correct answer involves marking cylinders with the Registration Identification Number (RIN) and the test date in a square pattern. This marking is crucial as it indicates that the cylinder has passed the Volumetric Expansion Method test, confirming its proper handling and safety for containing substances. The square pattern of the markings not only standardizes the appearance for easy recognition but also helps in maintaining a clear visual cue regarding the testing status and regulatory compliance of the container.

The use of a square pattern is significant as it differentiates it from other potential markings, making it simpler for inspectors and handlers to spot approved containers quickly. This practice aligns with safety regulations designed to minimize risks associated with the handling of pressurized cylinders.

Other marking conventions or requirements might not provide the same clarity or compliance checks that the square pattern establishes for identifying tested and certified cylinders, hence the emphasis on this format.