What is the Arc flash warning label?

Section 110.16 of the NEC 2011 code requires electrical equipment, such as switchboards, panelboards, industrial control panels, meter socket enclosures, and motor control centers, that are in other than dwelling occupancies, and are likely to require examination, adjustment, servicing, or maintenance while energized, shall be field marked to warn qualified personnel of potential electric arc flash hazards. The marking shall be located so as to be clearly visible to qualified personnel before examination, adjustment, servicing, or maintenance of the equipment.

There are two fine print notes shown below that are very important. 

FPN No. 1: NFPA 70E, Standard for Electrical Safety in the Workplace, provides assistance in determining severity of potential exposure, planning safe work practices, and selecting personal protective equipment. FPN No. 2: ANSI Z535.4, Product Safety Signs and Labels, provides guidelines for the design of safety signs and labels for application to products. 

The section 110.16 of the NEC clearly indicates that electrical equipment must be field marked and that NFPA 70E is to be used to determine the severity of the arc flash hazard and how to select personal protective equipment.  NFPA 70E states what should be on the arc flash label.