Sun sign? There are other planets that rule intelligence, which is needed to see through cults. Mercury is the one I can think of most, and when it is in Gemini or Virgo, and especially when tightly aspected with Uranus (the planet of rebellion), you are looking at someone that is likely to become apostate. And, Mercury in Gemini with Uranus in Virgo seems ideal for this--Mercury in Virgo and Uranus in Scorpio is another good sign (especially if they are near the same degree).
Those with Mercury in Sagittarius or Pisces, and especially with Uranus nowhere to be found, are at a disadvantage of becoming apostates. Also, if they have a strong Saturn (in Libra, Capricorn, or Aquarius) in the 5th or 7th natal house, they are more likely to be stuck. Plus, if Pluto is poorly aspected, they could be fated to remain jokehovian witlesses through this life only to be reincarnated in a Christian missionary family and stuck there in future lifetimes. (And if it conjuncts Zosma, or another bad star, that can make it even worse--especially with other planets adding to it).
As for sun signs, these are less powerful in keeping people in the cancer or getting them out. Mercury is the most powerful (ruling intelligence) along with Uranus (ruling rebellion) in this position. And, just hope that the moon was void of course when you get baptized, because that will tend to lead to the baptism failing.