This is an icon because it is an image representative of an object. When people see this picture they immediately associate it with mail. The unopened envelope means that there is a new piece of mail that has yet to be opened.
This image of biohazard waste is a symbol because it represents something to the person who sees it. When a person sees these images they think of danger and hazardous waste.
This image of a sign can be considered an index. This image of a person in a wheelchair signifies a handicap person. Add in the word parking underneath and it is a easily recognizable sign for handicap parking. The sign is always blue and always has the figure with the word parking beneath it to show the reserved parking spots for handicap people.
