Assuming you don't mind entering in the exact time and date of your birth, I think you can go to
www.astrology.com and enter your birthday in and then they will tell you your sun sign, your rising sign, and your moon sign. Then you can post your rising sign here if you want. It's up to you, and the information would definitely be considered sensitive so I could understand why a person wouldn't want to post it.
But I don't the info could conclusively prove identity because there are only 12x12x12 different combination of personality types so if you divide the number of combination people alive on the earth 6,774,705,647 by the number of possible personality types 1728 that still makes it difficult to prove your age and date of birth because it would make you an individual 1/3920547.249421296. (that's not actually correct because it would be the population at the year of your birth, which is variable)
A persons ip would be many times more revealing in that regard, and that's easy to find out. So I don't think it's such a big deal to reveal your sun sign, your rising sign, and your moon sign.
