These are hazard symbols used to show what is in the tanker and what the dangers are eg. toxic and corrosive
Many hazard warnings exist: flammable, corrosive, toxic, radioactive, explosive, etc.
Signs intended to warn you of a hazard may be called "safety signs" by some, and they are red and yellow in color. Safety signs that are intended to tell you that something is "safe" are green in color.
Do Google search for "DOT Placards".
It depends on what type of signs. On road signs they may be speed limits or distances; on tankers, they may be indicative of hazardous substances.
Hazard signs and the highway code are designed to help minimise the risk of accidents.
8 sings are there
animal hazard=sharp instrument hazard==heat hazard==glasses hazard==chemical hazard==electrical hazard==eye and face hazard==fire hazard==biohazard==laser radiation hazard==radioactive hazard==explosive hazard=
tell them to suck clock the tankers
hAZARDOUS
because of safety
OSHA is interested in posting signs because that is one way to increase the chances that employees who need to know about a hazard will get that information - from the signs.