The signs are styles of expression. Everyone has all 12 signs in their chart, because your natal chart has 12 houses and each of the signs rules one of the houses in your chart.
The 12 zodiac signs are derived from the elements and qualities in Astrology. The four elements are fire, earth, air and water. All the signs of an element have some core energy in common:
Fire – action, energy, vitality
Earth – resources, sensuality, reliability
Air – ideas, communication, people oriented
Water – emotion, intuition, passion
There are three qualities in Astrology and all signs of the same quality also have some energy in common:
Cardinal – initiating, drive, ambition
Fixed – focused, tenacious, definite
Mutable – versatile, restless, seeks change
When you combine these two you get twelve combinations:
Aries, Leo, and Sagittarius are all fire signs. They all have that fire energy in common. They differ though, because they each have a different quality. Aries is the most assertive of the three fire signs and has a sense of urgency and immediacy to it. Leo is more ambitions and driven. Sagittarius is the gypsy, seeking experiences.
Capricorn, Taurus and Virgo are the earth signs. Capricorn energy seeks accomplishment. Taurus desires comfort and doesn’t like waste. Virgo seeks to make things real and tangible.
Libra, Aquarius and Gemini are air. Libra energy leads people with ideas. Aquarius energy dives deeply into ideas to discover new ones. Gemini energy seeks to know something about everything.
Cancer, Scorpio and Pisces are water. Cancer energy controls through nurturing. Scorpio energy is consuming passion. Pisces energy blends with everything to create empathy.
People often have one element and quality that dominate their chart. So even if you have the Sun in Aries, if you have a lot of earth and mutable energy in your chart, your chart would have a Virgo feel to it, since Virgo is earth and mutable.
Even without seeing your chart, try to guess what element and quality you relate most to and then look at the sign that makes and see if you can feel that energy in you. It may not be your sun sign.
Now take a look at your chart and note how many pieces are in each element and quality. The sign that you come up with is called your signature and it is yet another layer to consider when you look at your chart.