Astrological Signs represent the medium of expression, while the Planets represent the energy of expression and the Houses represent the site of expression. If an artist is venting his frustration with society using spray paint on a concrete block, frustration is the planet, the concrete block is the House, and the spray paint is the Sign. The spray paint is serving to express the energy of anger. In Astrology, that is the role of the Signs. Each Sign represents a particular way of expressing energy, and adds a little bit of its own energy to the mix itself.
The most common use of the Astrological Sign is in determining one’s Sun Sign. A Sun Sign is the Zodiacal/Astrological Sign that the planet of the Sun was in during the time of the Astrological chart. The Sun Sign represents the prevailing trend of the chart, from which other things modify it, as the Sun as a planet represents the energy of Identity, and so whatever Sign the Sun is in is how the chart’s primary identity – and by extension, how the person or event the chart is for – expresses itself. The Sun Sign is the only factor in many horoscopes, but a true astrologer will tell you that just the Sun Sign means nothing. You need a full reading with Planets, Houses, and other Signs in order to fully understand a chart – and that is the art of Astrology.