Are there any requirements for the marking of electrical rooms? I feel it is a wonderful idea but have not found a specific requirement for this. My customer has tags on the wall beside doors identifying most rooms in their facility. I discovered several of the electrical rooms have no marking at all.

The only requirement I can think of is in the NEC requiring signage for electrical rooms having equipment over 1000V. I don't think there is a specific requirement besides what's in 110.21B.

Mike

IMO-
Yes, a "Notice" sign stating "authorized personnel only" should be installed, and is conservatively required.

Why would it be required?

The employer is required to provide a safe workplace.
It's likely that it is not clear what the hazards are in those rooms. And, once in the rooms, actions employees could take may increase the likelihood or create more hazards.

The employer would be required to either train all employees about interacting with the electrical equipment as part of an electrical safety program, to the level needed, or simply state in their employee handbook and or put up a sign that the employees would be required to follow as their duty. OSHA's requirements and the 70E deduce this.

A single sign on the door is less work and has more benefits than placing the same signage on every potential hazard, and is certainly easier and more safe than training them on interacting with the equipment.

Another thing to consider is Building and Fire Code requirements. These are not as easy to identify as there can be different requirements across regions/jurisdictions.

In Oregon, from the Structural Specialty Code:
2703.1 Labeling
Doors into electrical control panel rooms shall be marked with a plainly visible and legible sign stating "ELECTRICAL ROOM" or similar approved wording.
(This wording is similar to IFC section 603.4)
I also ensure 'Authorized Personnel Only' is on the signage.

If the room contains battery systems, I typically defer to IFC 1207.4.8 for signage requirements.