OSHA recognizeds two types of labeling in its Hazard Communications Standard, GHS and NFPA 704. GHS is the Globally Harmonized System of Classification and Labeling of Chemicals, and NFPA 704 refers to the National Fire Protection Association document 704, Identification of the Hazard of Materials for Emergency Response.
NFPA 704 provides an easily recognizable combination of color coding and numbers so that first responders can quickly identify the hazards associated with a certain product. The Hazard Communications Standard (HC2012) is an information system intended for those who work with chemicals on a routine basis.
Of the more confusing differences is the fact that NFPA 704 utilizes a numerical system for rating hazards, and the GHS system does, as well. However, NFPA 704 numbering is from 0-4 with 4 indicating the highest hazard. GHS numbering is from 1-4 with 4 indicating the lowest hazard.
NFPA has created a .pdf document that outlines these differences (image below). This document was created so that it could be printed, laminated, and utilized as a quick reference guide. Get the full document here, NFPA704/HC2012 Quick Card.