Is it an Emblem or a Symbol?

The words Emblem and Symbol are words that get used interchangeably and wrong so many times that I just want to scream.  Is there really that big of a difference?  YES!  Holy Calamari!  There is a difference that is big enough that it gets on my nerves when people use them wrong.  I am not entirely sure where people get the idea that these words can even be used as synonyms.  Most of the times they cannot be used interchangeably.

An emblem is tangible thing that is used to represent an abstract idea or a person.  For example:  the Ichthys is an emblem of Christ.  It represents him and people often put it on their cars to identify themselves as Christians.  I have one on mine.  Need another example?  Think of how you find statues and sculptures of the deities in the Hindu temples.  Those are emblems of their gods.  So, how is that different from a symbol?  A symbol is used as a substitute for something.  The skull and crossbones on a bottle of acid in a lab is a symbol that it is a poison.  A five pointed star can be used as a symbol to show that someone is a member of a law enforcement agency.  Here is the kicker about this.  Some things can be used as both.  The emblem of Islam is the crescent moon.  That is also a symbol of a certain moon phase in an almanac.  That skull that is used in the skull and crossbones symbol, it can be used as a symbol of how fragile human life can be. 

So the difference?  An emblem is used to represent an abstract idea in a concrete fashion.  A symbol is usually a picture that is used to represent a certain thing and is used as a substitution for a word or definition.  If in doubt, ask yourself if what you are trying to represent is an idea or if you are going to use it for substituting.