Does mercury have an NFPA 704 classification?
According to Sigma-Aldrich

Some symbols:


GHS06: Acute toxicity (oral, dermal, inhalation), categories 1,2,3
GHS08: Respiratory sensitization, category 1; Germ cell mutagenicity, categories 1A,1B,2; Carcinogenicity, categories 1A,1B,2; Reproductive toxicity, categories 1A,1B,2; Specific Target Organ Toxicity – Single exposure, categories 1,2; Specific Target Organ Toxicity – Repeated exposure, categories 1,2; Aspiration Hazard, category 1
GHS09: Hazardous to the aquatic environment; Acute hazard, category1; Chronic hazard, categories 1,2


And according to ScienceLab:


Health: 3
Fire: 0
Reactivity: 0


I believe the ScienceLab information is the 'NFPA 704 classification'.

EDIT****

An email exchange between NIST and myself asking for clarifiation:

My Email (Pre-filled form on the website, I don't have the original):

Something along the lines of "Hello, I see NIST and a few other manufactures
of have different NFPA classifications (I provided links to the SDS's), 
could you explain the difference between your ratings and theirs?"


Their response: 

Good afternoon,
Our NFPA rating Health = 2 Fire = 0 Reactivity = 0 matches other manufacturers.
You can check Aldrich website for 99.99 Mercury
http://www.sigmaaldrich.com/catalog/product/sigald/215457?lang=en&amp;region=US

Thank you,
Office of Reference Materials


Other manufacturers (Note, plural) apparently now equals 1 example