I hope zodiac signs won't be directly tied to personality or attraction. I hated how in TS1 and 2, I could never make a proper simself with both my real personality and my real zodiac sign, because Virgos had to be extremely neat and extremely introverted at the same time, and while the latter definitely applies to me, I'm anything but neat. I would prefer a system similar to pet breeds: Usually when you pick a breed in CAS, it comes with one or two predetermined traits, but they aren't set in stone. Likewise, when you choose a zodiac sign for your human sims, the game could suggest a base game trait stereotypically associated with that sign (like Family-Oriented for Cancer, Ambitious for Capricorn, etc.), but it's up to you whether you keep it or not.
Another idea that hasn't been explored yet, as far as I know, would be a relation between signs and skills. Leos are said to be very sociable, so they could have a natural Charisma booster, and it stacks with other bonuses that increase skill gain, so if your Leo also has the Quick Learner trait, completes the Social Butterfly child aspiration and reaches the top of the scout career, they will rush through the Charisma skill like nobody else who wasn't born under the same sign. But then again, if you want a Leo with no Charisma skill, you can simply choose not to have them build it. That way, it's just an optional benefit that may or may not influence your other plans, it's there, but not too intrusive.
As for how a sign is determined for a child born in-game, if you don't get to choose it yourself, it could be tied to the days of the week, because both weekdays and zodiac signs are tied to celestial bodies in our solar system. Friday, for example, is the day of Venus, and since Taurus and Libra are both signs of Venus, children born on Fridays could be one or the other. Of course, if they come up with fictional zodiac signs instead of using real ones, they can also make their own astrology system, but honestly, I wouldn't like that. I prefer real zodiac signs like we had in the past.
