You can find information on the distribution of birth days through the year. And yes, it is not even.
It seems you are curious on if members here at ZV is the same.
Just the idea of talking about zodiac sign is at the same level as astrology. That my life is determined by my birthday (why not the conception?) or the position of the planets - good grief.
I know my birthday, but what zodiac sign it is? quite uninteresting