Interpreting Art
There are certain recurring images that have been unearthed,
which are clues to ancient belief systems:

1)
Neolithic megaliths tend to have the following images: spirals,
concurrent circles, triangles, zig-zags, possible images of the sun
and moon in addition to people.  Look to the Monuments page for
illustrations.

2)
Iron Age and earlier finds show a preponderance of spoked
wheel symbols (representing the sun?).  Other Celtic finds include
swastikas, birds, double axes, rosettes, boars and bulls.

3) Certain themes recur when depicting deities:
horned gods, triple
gods/goddesses, mother goddesses
and animism.

4) The stag-god and the bull-horned god (worshipped in Northern
areas) are usually not seen with a consort, with a single exception
of a single site where he is shown with a horned goddess.  That
location is the site of Rutupiae.
The basic forms used to
decorate megalithic
monuments (left to right)
  1. dot/cupmark
  2. line
  3. circle
  4. quadrangle
  5. arc
  6. zigzag
  7. wavy line
  8. spiral
  9. oval
The Power of Three
Although this phrase does make people think of a specific TV series,
this phrase is extremely appropriate for the Celts as well.  
Repeatedly in art there are 3's - stellae and statues with 3 heads
(tricephalic), the triskele (a three way celtic knot, also can be see on
the above referenced show), triple goddesses, etc.
Sun as healer
Associating the sun with a healthy glow is an age old concept.
The Celts equated the sun god with healing.  Thus solar and
wheel images, especially on jewelry, often represent this power.
 (remember: an amulet cannot replace the protective power of a
good 48 SPF sunscreen)
Emphatically Torc-ed
Torcs (necklace seen to the left) helped to reinforce head worship.  
They could also be placed on the upper arms ritually extricating, as
a torc around the neck does, the top of the body from the rest