No real astrologer compares signs.
They do up YOUR personal uniique birthchart (full birthdate, exact time of birth, place of birth).
And then they do up the unique birthchart for the person you are wondering about.
And THEN they look to see if any of your 10 planets are some particular distance (synastry aspects) from any of their 10 planets. These "aspects" indicate interactions between two people, and some distances indicate harmony while others indicate discord.
We do NOT use Signs, and especially not Sun signs (which is what you , are asking about .. they are properly called "Sun-signs", not "star signs", nor "zodiac signs" ... and we call them Sun-signs to differentiate the from the Moon sign, the Mercury sign, the Venus sign, etc ... all the way out to the Pluto sign and the Rising/Ascendant sign).