ANSI Z535.2-2002 recommends the combination of upper and lower case sans serif text. Upper case only lettering may be used for short messages or emphasis of individual words.
Use Direct Statements:
Safety signs are intended to communicate information quickly enough to allow a person to understand it and take appropriate actions to avoid the hazard. Reaction times can be reduced by using the simplest and most direct statements possible.
Identifies the specific hazard with clear and simple language.
Use clear, accurate and simple language to warn persons of potential consequences if the warning is ignored.
A telephone number or other contact information should go on sign after the Action, Hazard description and consequences statements.