What's the difference between Signs and Symbols?

Sign
Something that stands for something else.

Glyph
A graphical representation of a character or part of a character in a font. A carved figure or character.

Symbol
Something that represents something else by association, resemblance, or convention. Something visible representing something invisible. A symbol can be embued with rich layers of meanings.

Icon
An idol. An image or representation. A religious image in the eastern church. A small clickable image representing files or programs in a computer.

Symbols: The Alphabet of Human Thought
A primer of terms categorizing symbols by use.
designhistory.org/symbols.html
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What Is the Meaning of Symbology?
Whether we know it or not, we interpret and respond to symbols all day, every day.
ehow.com/facts_6857527_meaning-symbology_.html

Icon - wikipedia.org
An icon is a religious work of art, most commonly a painting, from Eastern Christianity and in certain Eastern Catholic churches. More broadly the term is used in a wide number of contexts for an image, picture, or representation.
en.wikipedia.org/wiki/Icon
Symbol   

Symbols and the Search for Meaning
Although we hold a symbol language in common, we don't always interpret individual symbols in the same way. Symbols point to deeper truths that we usually experience as individuals or as members of a particular culture.
lyricalworks.com/symbols/aboutsymbols.htm