An example of a 'safety' sign from 1914, marking first aid.
Note: Exact legends were not provided in the Universal Safety Standards for 'safety' signs. "All safety signs... such as for exits, first aid equipment, etc., to consist of legible and conspicuous white letters on a green field, indicating the nature of the safety in as brief a form as possible."
Universal safety standards; a reference book of rules, drawings, tables, formulae, data and suggestions for use of architects, engineers, superintendents, foremen, inspectors, mechanics and students
Carl M. Hansen