The David-Andersen (D-A) Company is renowned for their stunning guilloche enameling.  The company made several series of zodiac-themed charms/pendants.  This hexagonal series is fun to collect.  The most common background colors are green and blue;  the purple and red are more unusual.  The charms in this series also exist in versions without enamel. D-A also made a set of round zodiac charms that seem to be a bit harder to come by.

Here are the birth signs depicted (all left to right):

First row:  Sagittarius, Gemini, Libra
Second row:  Aquarius, Aries, Scorpio
Third row:  Cancer, Virgo, Capricorn 
Fourth row:  Taurus, Leo, Pisces

You may recognize the Virgo charm from the cover of Charms and Charm Bracelets:  The Complete Guide.

American collectors tend to be puzzled by the D-A depiction of Cancer.  It turns out that the crayfish is the symbol for Cancer in Norway. 

These charms range in price from $25 - $35.  However, in the heat of the "battle" --- aka auction --- I've paid as much as $90 (!).