No one is A sign.
We have ALL 12 zodiac signs in our unique astrological birthchart.
What you are calling someone's "zodiac sign" is ONLY the Sign sun was moving through when they were born. The only part of your birthchart that can be found with just the month-day of birth and without extensive math computations.
Sun is only 2% of the entire personality.
And no two people with the same Sun sign will be the same, because no two people have the same birthchart.