Question: Does the mounting bracket need to be attached to the fire extinguisher for the vessel to pass the VSC?

Answer: As a VE, you know fire extinguishers are a required item under DECAL REQUIREMENTS. Mounting is under DISCUSSION ITEMS, therefore not required for a decal but is your job is to educate the importance of a mounted extinguisher, one that is always ready at a known location and cannot roll around and break and become faulty.