A skull and crossbones on a yellow background is a warning symbol that a material is what?

I thought it was a warning about being made by pirates, but that wasn't an option

D.O.T. Placard for Corrosives is black & white!

poison label is of a skull and crossbones on a white background. yellow background is an oxidizer, corrosive.

huh.. New York state blazing the trail of government regulations.. who would have guessed?