Is it a sin to just check out someones zodiac sign?

I assume you are talking about Christianity, since no other system deals with "sin". You really should learn the doctrines so you know things like this. It doesn't make any sense to claim to be a believer when you have no idea what you are supposed to believe. It is not reliable to ask people to tell you what the bible says. Many people will make up stuff because they don't know what it says, and many will make up stuff because they wish it would not say what it says. You just have to read it for yourself. Read a chapter of Proverbs every day. Proverbs has 31 chapters so you can keep your place by just looking at a calendar. There is no religion or nothing in Proverbs and you don't have to believe anything. Just read to find comfort and confidence. When you are comfortable with that, then read the bible from Romans to 2 Thessalonians over and over until you start to remember what it says. That is the part that applies to Christians. Here is a book to help you to understand the bible. It's a free download and you can get a hard copy at any bible book store.
philologos.org/__eb-htetb/ "How To Enjoy The Bible"

Straight answer to your question: Romans carefully explains that sins no longer count. Either you believe in Jesus and are saved, or you don't believe and are lost.