Christians believe in the will of God. Therefore, most Christians do not believe in luck. However, it also depends on Christians' view of God having a purpose for everything, or if they believe that God takes a step back, and uses what happens.

Is it a sin to believe in zodiac signs?

Participating in the belief of Zodiac signs is participating in astrology which throughout all of Scripture, the Bible condemns and God considers evil. Believing in zodiac signs is not wise.

Is it a sin to believe in karma?

Christians should not believe in karma because the sum of people's works does not decide whether they are saved or not. Only faith in Jesus Christ saves people from condemnation. Through God's grace, Christians are gifted a relationship with Jesus instead of the death they deserve.